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This guide provides a step-by-step approach for protecting Local Area Networks (LANs) and Wide Area Networks (WANs). The emphasis in this document is on the cost-effective security of LANs in a sensitive information environment. WANs are discussed as an extension of the LAN environment. The Computer Security Act of 1987 defines the term "sensitive information" as any information, the loss, misuse, disclosure, or modification of which could adversely affect the national interest, conduct of Federal programs, or the privacy to which individuals are entitled under the Privacy Act.

The Department of Health and Human Services (DHHS) depends on accurate and timely information to manage its broad range of programs and a budget of $525 billion for FY 1992. These programs and

payments touch the lives of most citizens. Virtually all vital information is processed in some form by computers - from the development of the DHHS budget, to the monitoring of health research grants, to the processing of individual entitlement payments. "We are at risk," advises the National Research

Council in Computers at Risk. "Although we trust them, computers are vulnerable - to the effects of poor design and insufficient quality control, to accident, and perhaps most alarmingly, to deliberate attack. The modern thief can steal more with a computer than with a gun. Tomorrow's terrorist may be able

to do more damage with a keyboard than with a bomb. To date, we have been remarkably lucky."

Connecting computers into networks significantly increases risk. Networks connect large numbers of users to share information and resources, but network security depends heavily on the cooperation of each user. Security is only as strong as the weakest link. A computer security study by the President's Council on Integrity and Efficiency (PCIE), chaired by the DHHS Inspector General, found that "virtually

all of the abuses and frauds [identified in the study] were carried out by authorized users, not outsiders." As the number, size, and complexity of DHHS LANs/WANs increase, cost-effective security becomes

a much more significant issue to deter fraud, waste, and abuse and to avoid embarrassment to the government.

This guide is intended to help LAN managers understand why they should be concerned about security, what their security concerns should be, and how to resolve their concerns. Section I of this document addresses the why, highlighting the basic statutory and Federal requirements for protecting LANs and introducing the concept of risk management. Due to the technical complexities of LANs, Section 2 briefly summarizes LAN components and features to serve as a foundation for discussing security requirements. Section 3 addresses what the LAN security requirements are in terms of the risk assessment process. Section 4 addresses how to implement LAN security step-by-step. The appendices

amplify Section 4 with specific examples that can be used. The result is a guide that can be tailored to specific LAN security requirements.


OMB has classified computer systems into two categories: general support systems and major applications. General support systems consist of hardware and software that provide general ADP or network support for a variety of users and applications. General support systems include LANs/WANs.

A LAN, or local area network, is a network of personal computers deployed in a small geographic area such as an office complex, building, or campus within the context of this discussion. A WAN, or wide area network, is an arrangement of data transmission facilities that provides communications capability across a broad geographic area (e.g., DIMES/FTS 2000).

More detailed definitions are listed in Appendix A. 1.3 FEDERAL SECURITY REQUIREMENTS FOR LANs/WANs 1.3.1Computer Security Act

The Computer Security Act of 1987, P.L. 100-235, dated January 8, 1988, requires Federal agencies to:

oidentify all computer systems that process sensitive data and prepare a plan for the security and privacy of each such system.

oprovide mandatory periodic training in computer security awareness and accepted security practices for all individuals who are involved in the management, use, or operation of Federal computer systems within or under the supervision of that agency.

1.3.2 Regulatory Requirements

The Office of Management and Budget (OMB) is chartered to enforce provisions of the Act, and is the principal Federal agency for automated information systems (AIS) security. OMB regulatory documents for security include: OMB Circular No. A-130, Appendix III, (Security of Federal Automated Information Systems); and OMB Circular No. A-123, (Internal Control Systems). OMB Bulletins provide detailed security guidance (e.g., OMB Bulletin 90-08, dated July 9, 1990).

The Computer Security Act of 1987 assigned the National Institute of Standards and Technology (NIST) the responsibility for developing computer security standards and guidelines for Federal unclassified systems, including LANs/WANs. Appendix B lists NIST publications applicable to LAN/WANs.

The Office of Personnel Management (OPM) provides guidance for designating sensitive positions and

screening the incumbents. The General Services Administration (GSA) issues its guidance in the Federal Information Resources Management Regulation (FIRMR). Please see Appendix B for OMB, NIST,

OPM, GSA, DHHS and other references applicable to LANs, and refer to the Department's AISSP Handbook for Federal security functions and additional information.

1.3.3 Departmental Security Policy

LANs/WANs come under the purview of the Departmental security policy:

DHHS will implement a Department-wide AIS security program to assure that each automated information system has a level of security that is commensurate with the risk and magnitude of the harm that could result from the loss, misuse, disclosure, or modification of the information

contained in the system. Each system's level of security must protect the confidentiality, integrity, and availability of the information. Specifically, this requires that:

a.each AIS have the appropriate technical, personnel, administrative, environmental, and telecommunications safeguards;

b.AIS security should be cost-effective; and AIS that supports critical OPDIV [Operating Division] functions has a contingency or

disaster recovery plan to provide continuity of operation.

Each OPDIV shall administer an AIS security program that meets statutory, regulatory, and Departmental requirements and the needs of the OPDIV and the public.


Risk management, as defined in the DHHS Automated Information Systems Security Program (AISSP)

Handbook, is a process for minimizing losses through the periodic assessment of potential hazards and the systematic application of corrective measures.

Risk to information systems is generally expressed in terms of the potential for loss. The greater the value of the assets, the greater the potential loss. Threats can be people (e.g., hackers, disgruntled employees, error-prone programmers, careless operators), things (e.g., unreliable hardware) or even

Nature itself (e.g., earthquakes, floods, lightning). Vulnerabilities are flaws in the protection of assets that can be exploited, partially or fully, by threats resulting in loss. "Safeguards" preclude or mitigate vulnerabilities.

"Managing risks means not only identifying threats but also determining their impact and severity. Some threats require extensive controls while others require few. Certain threats, such as viruses and other computer crimes, have been highlighted through extensive press coverage. On the other hand, repeated errors by employees may receive only minor consideration. Yet, statistics reveal that errors and omissions generally cause more harm than virus attacks. Resources are often expended on threats not

worth controlling, while other major threats receive little or no control. Until managers understand the magnitude of the problem and the areas in which threats are most likely to occur, protecting vital computer resources will continue to be an arbitrary and ineffective proposition."


This section provides a brief overview of the highly complex LAN/WAN environment to serve as a foundation for the discussion of network security matters in Section 3. The Department uses a mix of personal computers (PCs), LANs/WANs, terminals, minicomputers, and mainframes to meet its processing needs. DHHS LANs are primarily networks of PCs that come in many varieties and provide connectivity - directly or indirectly - to many of the Department's mini and mainframe computers.

A LAN is a group of computers and other devices dispersed over a relatively limited area and connected by a communications link that enables any device to interact with any other on the network. LANs commonly include microcomputers and shared (often expensive) resources such as laser printers and large hard disks. Although single LANs are geographically limited (to a department or office building, for example), separate LANs can be connected to form larger networks. Alternatively, LANs can be

configured utilizing a client-server architecture which makes use of "distributed intelligence" by splitting the processing of an application between two distinct components: a "front-end" client and a "back-end" server. The client component, itself a complete, stand-alone personal computer, offers the user its full range of power and features for running applications. The server component, which can be another

personal computer, minicomputer, or mainframe, enhances the client by providing the traditional strengths offered by minicomputers and mainframes in a time-shared environment: data management, information sharing among clients, and sophisticated network administration and security features.


PCs are an integral part of the LAN, using an adapter board, cabling, and software to access the data and devices on the network. PCs can also have dial-in access to a LAN via a modem and telephone line. The PC is the most vulnerable component of a LAN since a PC typically has weak security features (e.g., lack of memory protection), which will be discussed in more detail in Section 3.4, "Vulnerabilities."

LAN cabling provides the physical connections using twisted-pair cable, thin coaxial cable, standard

coaxial cable, or optical fiber (which provides the most security, as well as the highest capacity). Cabling is susceptible to tapping to gain unauthorized access to data, but this is considered unlikely due to the high cost of such action. A new alternative to cabling is a wireless LAN, which uses infrared light waves or various radio frequencies (RF) for transmission. Wireless LANs, like cellular radio, are vulnerable

to unauthorized interception.

Servers are dedicated computers, mostly PCs, that provide various support and resources to client workstations, including file storage, applications (e.g., e-mail), databases, and security services. In small peer-to-peer LANs, the server can function as one of the client PCs. In addition, minicomputers and mainframes can function in a true server mode. This shared processing is not to be confused with PCs

that serve as "dumb terminals" to access minis and mainframes. Controlling access to the server is a basic LAN security issue.

A network operating system is installed on a LAN server to coordinate the activities of providing services to the computers and other devices attached to the network. Unlike a single-user operating system, which performs the basic tasks required to keep one computer running, a network operating system must acknowledge and respond to requests from many workstations, managing such details as

network access and communications, resource allocation and sharing, data protection, and error control. The network operating system provides crucial security features for a LAN. See Section 2.8, Access Control Mechanisms, for a discussion of these security features.

Input/output devices (e.g., printers, scanners, faxes) are shared resources available to LAN users and are susceptible to security problems (e.g., sensitive output left unattended on a remote printer).

A Backbone LAN interconnects the small LAN work groups. For example, DHHS/Office of the

Secretary (OS) uses copper and fiber optic cabling for their backbone circuits. Fiber optics provides a high degree of security (e.g., the light signals are difficult to tap or otherwise intercept).

Internetworking devices include repeaters, bridges, routers, and gateways. These are communications devices for LANs/WANs that provide the connections, control, and management for efficient and reliable

internetwork access. These "traffic cops" can also have security control features for regulating access.


A PC that is not physically connected by cables to a LAN may be permitted dial-in access via a modem

and telephone line.

A PC dial-in connection can be made directly to a LAN server. This connection can occur when a server has been fitted with a dial-in port capability. The remote PC requires communications software, a modem/telephone line, and the LAN dial-in number to complete the connection. This access procedure invokes the LAN access control measures such as logon/password requirements. LANs usually have specific controls for remote dial-in procedures. The remote unit used to dial-in may be any computer, including a lap-top PC.

A PC can remotely control a second PC via modems and software such as pcAnywhere or Carbon Copy. When this second PC is cabled to a LAN, a remote connection can be made from the first PC through

the second PC into the LAN. The result is access to the LAN within the limits of the user's access controls. One example of this remote control access is when an individual uses a home computer to dial in to his/her office PC and then remotely controls the office PC to access the LAN. (The office PC may also be left running to facilitate the connection.) It should be noted that the LAN may not have the capability to detect that a remote control session is taking place.

Dial-in capabilities increase the risk of unauthorized access to the system, thereby requiring strong password protection and other safeguards, such as callback devices, which are discussed in Section 3.4.3.


The topology of a network is the way in which the PCs on the network are physically interconnected. Network devices can be connected in specific patterns such as a bus, ring, or star or some combination of these. The name of the topology describes its physical layout.

In a star configuration, PCs communicate through a central hub device. Regarded as the first form of local area networking, the star network requires each node to have a direct line to the central or shared hub resource.

In a ring network, messages circulate the loop, passing from PC to PC in bucket-brigade fashion. IBM's Token-Ring network is an example, which uses a special data packet called a "token." Only one token exists on the network at any one time, and the station owning the token is granted the right to communicate with other stations on the net. A pre-defined token-holding time keeps one user from monopolizing the token indefinitely. When the token owner's work is completed or the token-holding time has run out, the token is passed to the next user on the ring.

PCs on a bus network send data to a head-end retransmitter that rebroadcasts the data back to the PCs.

LAN topology has security implications. For example, in sending a sensitive data message from one user to another, the star topology sends it directly through the hub to the receiver; in the ring and bus topologies, the message is routed past other users.


A protocol is a formal set of rules that computers use to control the flow of messages between them. Networking involves such a complex variety of protocols that the International Standards Organization (ISO) defined the now-popular seven layer communications model. The Open Systems Interconnection

(OSI) model describes communication processes as a hierarchy of layers, each dependent on the layer beneath it. Each layer has a defined interface with the layer above and below; this interface is made flexible so that designers can implement various communications protocols - with security features - and still follow the standard. Here is a very brief summary of the layers, as depicted in Figure 2-1, OSI Model:

oThe application layer is the highest level. It interfaces with

users, gets information from databases, and transfers whole

files. (E-mail is an application at this level.)

oThe presentation layer defines how applications can enter the network.

oThe session layer makes the initial contact with other computers and sets up the lines of communication. (This layer allows devices to be referenced by name rather than by network address.)

oThe transport layer defines how to address the physical

locations/devices on the network, make connections between nodes, and handle the internetworking of messages.

oThe network layer defines how the small packets of data are routed and relayed between end systems on the same network or on interconnected networks.

oThe data-link layer defines the protocol that computers must follow to access the network for transmitting and receiving messages. (Token Ring and Ethernet operate within this layer and the physical layer, defined below.)

oThe physical layer defines the physical connection between the computer and the network, and converts, for example, the bits into voltages or light impulses for transmission. (Topology is defined here.)

Bridges, routers, and gateways are "black boxes" that permit the use of different topologies and protocols within a single heterogenous system. In general, two LANs that have the same physical layer protocol, can be connected with a simple, low-cost repeater. Two LANs that speak the same data-link layer protocol, can be connected with a bridge - even if they differ at the physical layer. If the LANs have a common network layer protocol, they can be connected with a router. If two LANs have nothing in common, they can be connected at the highest level, the application layer, with a gateway.

These "black boxes" have features and "filters" that can enhance network security under certain conditions, but the features must be understood and utilized. "For example, an organization could elect to permit electronic mail (e-mail) to pass bidirectionally by putting in place a mail gateway while preventing interactive log-in sessions and file sessions (by not passing any other traffic than e-mail)."

FIPS PUB 146-1, Government Open Systems Interconnection Profile (GOSIP), specifies a set of OSI protocols for computer networking that is intended for acquisition and use by government agencies. "GOSIP does not mandate that government agencies abandon their favorite computer networking

products. GOSIP does mandate that government agencies, when acquiring computer networking

products, purchase OSI capabilities in addition to any other requirements, so that multi-vendor interoperability becomes a built-in feature of the government computing environment, a fact of life in conducting government business."

FIPS PUB 146-1, Chapter 6 (Security Options) and Appendix 1 (Security) discuss the security options in GOSIP. Three points are extracted for LAN/WAN management guidance:7

oSecurity is of fundamental importance to the acceptance and use of open systems. Part 2 of the Opens Systems Interconnection reference model (Security Architecture) is now an international standard (IS 7498/2). The standard describes a general architecture for security in OSI, defines a set of security services that may be supported within the OSI model, and outlines a number of mechanisms that can be used in providing the services. However, no protocols, formats or minimum requirements are contained in the standard.

oAn organization desiring security in a product that is being purchased in accordance with this profile must specify the security services required, the placement of the services within the OSI architecture, the mechanisms to provide the services, and the management features required.

oSecurity is an option in GOSIP. As such, security services may be provided at one or more

of the layers 2,3,4,6, and 7. The primary security services that are defined in the OSI security architecture are:

-Data confidentially services protect against unauthorized disclosure.

-Data integrity services protect against unauthorized modification, insertion, and


-Authentication services verify the identity of communication peer entities and the

source of data.

-Access control services allow only authorized communication and system access. -Non-repudiation with proof of origin provides to the recipient proof of origin of data

and protects against any attempt by the originator to falsely deny sending the data or its contents.


Applications on a LAN can range from word processing (e.g., WordPerfect) to database management systems (e.g., ORACLE, dBASE). The most universally used application is e-mail.

E-mail software provides a user interface to help construct the mail message and an "invisible" engine to move the e-mail to its destination. Depending on the address, the e-mail may be routed across the office via the LAN or across the country via LAN/WAN bridges and gateways. E-mail may also be sent to other mail systems, both mainframe and PC-based, such as cc:Mail, which is in use at SSA. Text or

binary files can be attached to e-mail. An important security note is that, on some systems, it is also possible to restrict mail users from attaching files (as a part of an anti-virus program, for instance).

Many application systems have their own set of security features, in addition to the protection provided by the network operating system. Database management systems in particular have comprehensive security controls to limit access to authorized users.

2.6 The WAN

A natural extension of the LAN is the wide area network (WAN). A WAN connects remote LANs and

ties remote computers together over long distances. The WAN provides the same functionality as the individual LAN, but on a larger scale - electronic mail, applications, and files can now move throughout the organization-wide internet. WANs are, by default, heterogeneous networks that consist of a variety of computers, operating systems, topologies, and protocols. The most popular internetworking devices for WANs are bridges and routers. Hybrid units called brouters, which provide both bridging and routing functions, are also appearing. The decision to bridge or route depends on protocols, network topology, and security requirements. Internetworking schemes often include a combination of bridges and routers.

The DHHS Departmental Information Management Exchange System (DIMES) is the wide area network

for the Department, operated on a fee-for-service basis by the Public Health Service's Parklawn Computer Center (PCC). The DIMES network topology is a physical star, with the PCC as the hub. The PCC

uses the FTS 2000 Digital Transmission Service for its backbone communications.

DIMES has evolved over the past decade to support a variety of networking capabilities for organizations within DHHS. These include: LAN to LAN interconnection, gateways to other government and private sector networks, and e-mail backbone capabilities. Network management and security services include long-haul data encryption (DES).

Figure 2-2, below, illustrates a basic LAN/WAN, connecting a Banyan LAN to the Parklawn Computer Center via DIMES. In this configuration, the Communications Server performs the routing functions

for the LAN under the direction of the network operating system. No bridges are used in this configuration. While repeaters are not shown on the diagram, they are used on the Work Group LAN rings when required by distance factors.


The overall management of a LAN/WAN is highly technical. The International Standards Organization's (ISO) network management model divides network management functions into five subsystems: Fault Management, Performance Management, Configuration Management, Accounting Management, and

Security Management. Security management includes controlling access to network resources.

Network management products, such as monitors, network analyzers, and integrated management

systems, provide various network status and event history data. These and similar products are designed for troubleshooting and performance evaluation, but can also provide useful information, patterns, and trends for security purposes.

For example, a typical LAN analyzer can help the technical staff troubleshoot LAN "bugs" (usually decoding all seven layers of the ISO reference model), monitor network traffic, analyze network protocols, capture data packets for analysis (but usually does not decode data), and assist with LAN expansion and planning. For example, while LAN audit logs can record the user identification code of someone making excessive logon errors (which might not be the owner), it may require a network

analyzer to determine the exact identity of the PC on which the logon errors are occurring. As passive monitoring devices, network analyzers do not log on to a server and are not subject to server-software security. Therefore, analyzer operators should be appropriately screened.


Network operating systems have access control mechanisms that are crucial for LAN/WAN security. For

example, access controls can limit who can logon, what resources will be available, what each user can do with these resources, when and from where access is available. Management, LAN, security, and key user personnel should cooperate closely to implement access controls. The Banyan Vines (4.X) security procedures, User Security, Network File Access, Console Security, and Network Security, are highlighted

below to illustrate the range of security that a LAN can provide. Similar functions are provided by other products, such as Novell NetWare Security Services.

User Security. User access controls determine how, when, and where LAN users will gain

access to the system. Setting up user security profiles includes the following tasks:

oSpecify group security settings

oSpecify settings for specific users

oManage password security - length, expiration, etc. oPrevent user changes to settings

oSpecify logon settings

oSpecify logon times

oSpecify logout settings

oSpecify, modify, and delete logon locations (workstation, server, and link)

oDelete a user's security

oSpecify user dial-in access lists for servers

Network File Access. File security is determined by the level of security that is imposed on the directory in which the file resides. (Individual files can be secured by employing "password protection" or other security mechanisms allowed by the specific application software.) Each directory has an access rights list (ARL) that consists of an ordered series of StreetTalk names (users) and access levels. There are four levels of access:

oControl - the user can assign access rights on directories and subdirectories; create, modify, read, and delete files and subdirectories.

oModify - the user can create, modify, read, and delete files and subdirectories.

oRead - the user can read and copy (and execute) any file within a directory.

oNull - prevents user access to a particular directory. This access right is for protecting sensitive information. (Any user not included in a directory's access rights list, directly by name or indirectly by group or list membership, has null access - which

can be changed by system administrators, i.e., control access.)

Console Security. The console security/selection function allows the system administrator to prevent unauthorized persons from using the operator console. This function allows the system administrator to assign a console password, lock and unlock the console, and change the console type (i.e., assign operator functions to a workstation).

Network Security. These controls determine how outside users and servers can access the resources in the LAN over dial-up lines or intermediate networks or wide area networks. Network security tasks include:

oSpecifying user dial-up access

oSpecifying internetwork access


The future direction of DHHS computing is increased information sharing across the Department. A host of technologies are evolving to assist the Department in reaching this goal: powerful computers connected to large bandwidth circuits to move huge amounts of information, open systems architectures to connect various hardware systems, portability of software across multiple systems, and desk-top multi-media capabilities, to name just a few.

The center of these evolving technologies is the LAN/WAN. Departmental networks will continue to

grow rapidly, becoming the lifeline of Departmental activity. The goal is to provide transparent access to Departmental data across mainframes, minicomputers, and PCs. Network security must increase commensurately. The key is to balance information sharing with information security. The

information systems security officers (ISSOs) for the LAN environment of tomorrow will, by necessity, require a high degree of technical hardware and software knowledge.



A risk analysis is a formalized exercise that includes:

· Identification, classification, and valuation of assets; o

· Postulation and estimation of potential threats;

· Identification of vulnerabilities to threats; and

· Evaluation of the probable effectiveness of existing safeguards and the benefits of additional safeguards.


3.2.1 Protection Needed

The purpose of this section is to determine the type and relative importance of protection needed for the LAN. Based on OMB guidance, a LAN system and its applications may need protection (e.g., administrative, physical, and technical safeguards) for one or more of the following reasons:

Confidentiality. The system contains information that requires protection from unauthorized disclosure. Examples: the need for timed dissemination, as with the DHHS Budget, personal data covered by the Privacy Act, and proprietary business information.

Integrity. The system contains information that must be protected from unauthorized,

unanticipated, or unintentional modification, including the detection of such activities. Examples: systems critical to safety or life support and financial transaction systems.

Availability. The system contains information or provides services that must be available on a timely basis to meet mission requirements or to avoid substantial losses. (One way to estimate criticality of a system is in terms of downtime. If a system can be down for an extended period at any given time, without adverse impact, it is likely that it is not within the scope of the availability criteria.)

For each of the three categories (confidentiality, integrity, and availability), it is necessary to determine if the protection requirement is:

· High - a critical concern of the organization.

· Medium - an important concern, but not necessarily paramount in the organization's priorities.

· Low - some minimal level of security is required, but not to the same degree as the previous two categories.

Refer to the DHHS AISSP Handbook, Chapter II, Security Level Designations, for more detail concerning sensitive security levels.

3.2.2 Asset Values

A valuation process is needed to establish the "risk" or potential for loss in terms of dollars. The greater the value of the assets, the greater the potential loss, and therefore, the greater the need for security. Asset values are useful indicators for evaluating appropriate safeguards for cost-effectiveness, as required by OMB Circular Number A-130, but they do not reflect the total tangible and intangible value of information systems. The cost of re-creating the data or information could be more than the hardware costs. The violation of confidentiality, the unauthorized modification of important data, or the denial of services at a crucial time could result in substantial "costs" that are not measurable in monetary terms alone. For example, the accidental or intentional release of premature or partial information relating to investigations, budgets, or contracts could be highly embarrassing to government officials and cause loss of public confidence in the government.

Asset valuation should include all computing-associated tangible assets, including computer hardware, special equipment, and furnishings. Software, data, and documentation are generally excluded since

backup copies should be available.

The starting point for asset valuation is the LAN inventory. A composite summary of inventory items, acquisition value, current depreciated value, and replacement value is one way to provide a reasonable

basis for estimating cost-effectiveness for safeguards. It should be noted that if a catastrophic loss were to occur, it is unlikely that any organization would replace all hardware components with exact model equivalents. Instead, newer substitute items currently available would probably be chosen, due to the rapid pace of technological improvements.


A threat is an identifiable risk that has some probability of occurring.

A useful framework for introducing the discussion of threats is depicted in Figure 3-1, Security Threats. People threats are by far the largest category and most of the people are insiders - employees who make errors and omissions, and employees who are disgruntled or dishonest.

People threats are costly. Employee errors, accidents, and omissions cause some 50 to 60 percent of the annual dollar losses. Disgruntled employees and dishonest employees add another 20 percent. These insider threats are estimated to account for over 75 percent of the annual dollar loss experienced by organizations each year. Outsider threats such as hackers and viruses add another 5 percent. Physical threats, mainly fire and water damage, add

another 20 percent. It should be noted that these figures were published in 1988, and since that time there has been a dramatic increase in virus incidents, which may significantly enlarge the dollar loss from outsider threats, particularly in the LAN environment.

In this paper, threats are grouped in three broad areas: People threats, virus threats, and physical threats. LANs are particularly

susceptible to people and virus related threats because of the large number of people who have access rights.

3.3.1 People Threats

People threats include the following:

System Administration Error: all human

errors occurring in the setup, administration, and operation of LAN systems, ranging from the failure to properly enable access controls and other security features to the lack of adequate backups. The

possible consequences include loss of data confidentiality, integrity, and system availability, as well as possible embarrassment to the government or the individual.

PC Operator Error: all human errors occurring in the operation of PC/LAN systems, including

improper use of logon/passwords, inadvertent deletion of files, and inadequate backups. Possible consequences include data privacy violations and loss of capabilities (such as the accidental erasure of critical programs or data).

Software/Programming Error: all the "bugs," incompatibility issues, and related problems that occur

in developing, installing, and maintaining software on a LAN. Possible consequences include degradation, interruption, or loss of LAN capabilities.

Unauthorized Disclosure: any release of sensitive information on the LAN that is not sanctioned by proper authority, including those caused by carelessness and accidental release. Possible consequences are violations of law and policy, abridgement of rights of individuals, embarrassment to individuals and the government, and loss of public confidence in government.

Unauthorized Use: employment of government resources for purposes not authorized by the Agency and

the use of non-government resources on the network (such as using personally-owned software at the office). Possible consequences include the introduction of viruses, and copyright violations for use of unlicensed software. (See DHHS AISSP Handbook for policy guidance).

Fraud/Embezzlement: the unlawful deletion of government recorded assets through the deceitful manipulation of government controls, files and data, often through the use of a LAN. Possible consequences include monetary loss and wrongful contract/grant awards.

Modification of Data: any unauthorized changing of data, which can be motivated by such things as personal gain, favoritism, a misguided sense of duty, or a malicious intent to sabotage. Possible consequences include the loss of data integrity and potentially flawed decision making. A high risk is the disgruntled employee.

Alteration of Software: any unauthorized changing of software, which can be motivated by such things as disgruntlement, personal gain, or a misguided sense of duty. Possible consequences include all kinds of processing errors and loss of quality in output products.

Theft of ADP Assets: the unauthorized/unlawful removal of data, hardware, or software from

government facilities. Possible consequences for the loss of hardware can include the loss of important data and programs resident on the hard disk or on diskettes stored in the immediate vicinity.

3.3.2 Viruses and Related Threats

"Computer viruses are the most widely recognized example of a class of programs written to cause some form of intentional disruption or damage to computer systems or networks. A computer virus performs two basic functions: it copies itself to other programs, thereby infecting them, and it executes the

instructions the author included in it. Depending on the author's motives, a program infected with a virus may cause damage immediately upon its execution, or it may wait until a certain event has occurred, such as a particular time or date. The damage can vary widely, and can be so extensive as to require the complete rebuilding of all system software and data. Because viruses can spread rapidly to other programs and systems, the damage can multiply geometrically."

"Related threats include other forms of destructive programs such as Trojan horses and network worms. Collectively, they are known as malicious software. These programs are often written to masquerade as useful programs, so that users are induced into copying them and sharing them with their friends. The malicious software phenomena is fundamentally a people problem, as it is [frequently] authored and [often] initially spread by individuals who use systems in an unauthorized manner. Thus, the threat of unauthorized use, by unauthorized and authorized users, must be addressed as a part of virus prevention."14

3.3.3 Physical Threats

Electrical power problems are the most frequent physical threat to LANs, but fire or water damage is the most serious. Physical threats include the following:

Electrical Power Failures/Disturbances: any break or disturbance in LAN power continuity that is sufficient to cause operational interruption, ranging from high-voltage spikes to area "brownouts." Possible consequences range from minor loss of input data to temporary shutdown of systems.

Hardware Failure: any failure of LAN components (particularly disk crashes in PCs). Possible

consequences include loss of data or data integrity, loss of processing time, and interruption of services; may also include degradation or loss of software capabilities.

Fire/Water Damage: the major catastrophic destruction of the entire building, partial destruction within

a zone, LAN room fire, water damage from sprinkler system, and/or smoke damage. The possible

consequences include loss of the entire system for extended periods of time.

Other Physical Threats: Environmental failures/mishaps involving air conditioning, humidity, heating, liquid leakage, explosion, and contamination. Physical access threats include sabotage/terrorism, riot/civil disorders, bomb threats, and vandalism. Natural disasters include flood, earthquake, hurricane, snow/ice storm, windstorm, tornado, and lightning.


Vulnerabilities are flaws in the protection of LANs/WANs that can be exploited, partially or fully, by threats resulting in loss. Only a few generic vulnerabilities will be highlighted here, since vulnerabilities are specific weaknesses in a given LAN environment. Vulnerabilities are precluded by safeguards, and

a comprehensive list of LAN safeguards is discussed in Section 3.5, "Safeguards." Of paramount

importance is the most basic safeguard: proper security awareness and training.

A LAN exists to provide designated users with shared access to hardware, software, and data. Unfortunately, the LAN's greatest vulnerability is access control. Significant areas of access vulnerability include the PC, passwords, LAN server, and internetworking.

3.4.1 PC

The PC is so vulnerable that user awareness and training are of paramount importance to assure even a minimum degree of protection. PC vulnerable areas include:

Access Control. Considerable progress has been made in security management and technology for large-

scale centralized data processing environments, but relatively little attention has been given to the protection of small systems. Most PCs are single user systems and lack built-in hardware mechanisms that would provide users with security-related systems functions. Without such hardware features (e.g.,

memory protection), it is virtually impossible to prevent user programs from accessing or modifying parts of the operating system and thereby circumventing any intended security mechanisms.

PC Floppy Disk Drive. The floppy disk drive is a major asset of PC workstations, given its virtually unlimited storage capacity via the endless number of diskettes that can be used to store data. However, the disk drive also provides ample opportunity for sensitive government data to be stolen on floppy disks and for computer viruses to enter the network from literally hundreds of access points. This problem is severe in certain sensitive data environments, and the computer industry has responded with diskless workstations designed specifically for LAN operations. The advantage of diskless PCs is that they solve certain security problems, such as the introduction of unauthorized software (including viruses) and the unauthorized removal of sensitive data. The disadvantage is that the PC workstation becomes a limited, network-dependent unit, not unlike the old "dumb" mainframe terminals.

Hard Disk. Most PCs have internal hard disks ranging from 10 to 160 or more megabytes of on-line storage capacity. Sensitive data residing on these hard disks are vulnerable to theft, modification, or destruction. Even if PC access and LAN access are both password protected, some PCs may be booted

from a floppy disk that bypasses the password, permitting access to unprotected programs and files on the hard disk. PC hardware and software security features and products are available to provide increasing degrees of security for data on hard disk drives, ranging from password protection for entering the system to data encryption.

"Erasing" hard disks is another problem area. An "erase" or "delete" command does not actually delete

a file from the hard disk. It only alters the disk directory or address codes so that it appears as if deletion or erasure of the data has taken place. The information is still there and will be electronically "erased" when DOS eventually writes new files over the old "deleted" files. This may take some time, depending

on the available space on the hard disk. In the meantime, various file recovery programs can be used

to magically restore the "deleted" file. There are special programs that really do erase a file and these should be used for the removal of sensitive files. A companion issue is that the server may have a copy of the sensitive file, and a user may or may not have erase privileges for the server files.

Repairs. Proper attention must be given to the repair and disposition of equipment. Commercial repair staff should be monitored by government technical staff when service is being performed on sensitive PC/LAN equipment. Excess or surplus hard disks should be properly erased prior to releasing the equipment.

3.4.2 The PC Virus

PCs are especially vulnerable to viruses and related malicious software (e.g., Trojan horse, logic bomb, worm). An executing program, including a virus-infected program, has access to most things in memory

or on disk. For example, when DOS activates an application program on a PC, it turns control over to the program for execution. There are virtually no areas of memory protected from access by application programs. There is no block between an application program and the direct usage of system input/output (disk drives, communications, ports, printers, screen displays, etc.). Once the application program is running, it has complete access to everything in the system.

Virus-infected software may have to be abandoned and replaced with uninfected earlier versions. Thus, an effective backup program is crucial in order to recover from a virus attack. Most important, it is essential to determine the source of the virus and the system's vulnerability and institute appropriate safeguards.

A PC LAN is also highly vulnerable, because any PC can propagate an infected copy of a program to other PCs and possibly the server(s) on the network.

3.4.3 LAN Access

Access Control. A password system is the most basic and widely used method to control access to LANs/WANs. There may be multiple levels of password controls (i.e., to the LAN and its services) for access to each major application on the LAN, and to other major systems interconnected to the LAN. Conversely, some system access controls depend heavily on the initial LAN logon/password sequence. While passwords are the most common form of network protection, they are also the weakest (from a human aspect). Studies by NIST and other organizations have found that passwords have many weaknesses, including: poor selection of passwords by users (e.g., middle names, birthdays), poor password administration (e.g., no password guidance, no requirement to change passwords regularly),

and the recording of passwords in easily detected formats (on calendar pads, in DOS batch files, and even in logon sequences). Group/multi-user passwords lack accountability and are also vulnerable to misuse.

Dial-in Access. Dial-in telephone access via modems provides a unique "window" to LANs, enabling anyone with a user ID, password, and a computer (e.g., PC, terminal, or lap-top PC) to log into the

system. Hackers are noted for their use of dial-in capabilities for access, using commonly available user IDs and cleverly guessing passwords. Effective passwords and logon procedures, dial-in time limitations and locations, call back devices, port protectors, and strong LAN administration are ways to provide dialin access control.

UNIX. UNIX is a popular operating system that is often cited for its vulnerabilities, including its handling of "superusers." Whoever has access to the superuser password, has access to everything on

the system. NIST Interagency Report 4453 states that UNIX was not really designed with security in mind. "To complicate matters, new features have been added to UNIX over the years, making security

even more difficult to control. Perhaps the most problematic features are those relating to networking: remote logon, remote command execution, network file systems, diskless workstations, and electronic mail. All of these features have increased the utility and usability of UNIX by untold amounts. However, these same features, along with the widespread connection of UNIX systems to the Internet

and other networks, have opened up many new areas of vulnerabilities to unauthorized abuse of the system."

3.4.4 Internetworking

Access Control. Internetworking is the connection of the local LAN server to other LAN/WAN servers via various connection devices (e.g., routers, gateways). The current Departmental e-mail system, for example, could not exist without this interconnectivity. Each additional LAN/WAN interconnection can add outside users and increase the risks to the system. LAN servers and network devices can function

as "filters" to control traffic to and from external networks. For example, application gateways may be used to enforce access control policies at network boundaries. The important point is to balance connectivity requirements with security requirements.

Wireless LANs. Wireless LANs use infrared light waves or radio frequencies (RF) to transmit signals and data to PCs, servers, and other network devices. Networks can use a combination of wired and wireless capabilities. Increasingly, portable computers, laptops, and palmtops will have wireless connectivity. Wireless LANs, particularly those which are radio based, can be vulnerable to the

interception of data and passwords. Security planning, careful selection of security features (e.g., data encryption), and security training are crucial for a successful wireless LAN implementation.

Organizational Teamwork. The effective administration of LANs/WANs requires inter-organizational coordination and teamwork. Since networks can cross so many organizational boundaries, integrated security requires the combined efforts of many personnel, including the administrators and technical staff (who support the local servers, networks, and internetworks), security personnel, users, and management.

E-mail. E-mail messages are somewhat different from other computer applications in that they can involve "store and forward" communications. Messages travel from the sender to the recipient, often from one computer to another over a WAN. When messages are stored in one place and then forwarded

to multiple locations, they become vulnerable to interception or can carry viruses and related malicious software.

Figure 3-2 highlights LAN vulnerabilities.


Safeguards preclude or mitigate LAN vulnerabilities and threats, reducing the risk of loss. No set of safeguards can fully eliminate losses, but a well-planned set of cost-effective safeguards can reduce risks

to a reasonable level, as determined by management. To make this guide as useful as possible, safeguards will be presented and discussed in the categories suggested by OMB for security plans. Most of these safeguards also apply to applications.

3.5.1 General Safeguards

Assignment of LAN Security Officer. The first safeguard in any LAN security program is to assign

the security responsibility to a specific, technically knowledgeable person. This person must then take the necessary steps to assure a viable LAN security program, as outlined herein and in the AISSP Handbook. Also, the Handbook requires that a responsible owner/security official be assigned to each application, including e-mail and other LAN applications.

Security Awareness and Training. Security training is mandated by the Computer Security Act of 1987. All Federal employees and contractors involved with the management, use, design, acquisition, maintenance or operation of a LAN must be aware of their security responsibilities and trained in how to fulfill them. See the DHHS AIS Security Training and Orientation Program (AIS-STOP) Guide for detailed guidance on security training programs.

Technical training is the foundation of security training. These two categories of training are so interrelated that training in security should be a component of each computer systems training class. Proper technical training is considered to be perhaps the single most important safeguard in reducing human errors -- the mistakes of otherwise well-meaning employees.

Personnel Screening. Personnel security policies and procedures should be in place and working as part of the process of controlling access to LANs. Specifically, LAN management must designate sensitive positions and screen incumbents, following the guidance in DHHS Instruction 731-1, Personnel Manual, Personnel Security/Suitability - Policy and Guidance, August 4, 1988, for individuals involved in the management, operation, security, programming, or maintenance of the system. In the PCIE computer security study, cited earlier in Section 1.1, fraud and abuse was often committed by authorized government/contractor users (not outsiders), and "it was also determined that over one-fifth of them had criminal records prior to being hired."

The personnel screening process should also address LAN repair and maintenance activities, as well as janitorial and building repair crews that may have unattended access to LAN facilities.

Separation of Duties. People within the organization (insider people threats) are the largest category of risk to the LAN. Separation of duties is a key to internal control, designed to make fraud or abuse

difficult without collusion. For example, setting up the LAN security controls, auditing the controls, and management review of the results should be performed by different persons.

Preventive Maintenance. Hardware failure is an ever present threat, since LAN physical components

wear out and break down. Preventive maintenance identifies components nearing the point at which they could fail, allowing for the necessary repair or replacement before operations are affected.

Written Procedures. It is human nature for people to perform tasks differently and inconsistently, even if the same person performs the same task. An inconsistent procedure increases the potential for an unauthorized action (accidental or intentional) to take place on a LAN. Written procedures help to establish and enforce consistency in LAN operations.

Procedures should be tailored to specific LANs and addressed to the actual users, to include the "do's" and "don't's" of the main elements of safe computing practices, such as: access control (e.g., password

content), handling of floppies, copyrights and license restrictions, remote access restrictions, input/output controls, checks for pirated software, courier procedures, and use of lap-top computers.

3.5.2 Technical Safeguards

These are the hardware and software controls, as basically defined in OMB Bulletin 90-08, to protect the LAN from unauthorized access or misuse, help detect security violations, and provide security for LAN applications.

User Identification and Authentication. User identification and authentication (verification) controls

are used to verify the identity of a station, originator, or individual prior to allowing access to the system, or specific categories of information within the system. Identification involves the identifier or name

by which the user is known to the system (e.g., a user identification code). This identifying name or number is unique, is unlikely to change, and need not be kept secret. When authenticated, it is used to provide authorization/access and to hold individuals responsible for their subsequent actions.

Authentication is the process of "proving" that the individual is actually the person associated with the identifier. Authentication is crucial for proper security; it is the basis for control and accountability in a system. There are three basic authentication methods for establishing identity:

o Something known by the individual: Passwords are presently the most commonly used

method of controlling access to systems. Passwords are a combination of letters and numbers

(or symbols), preferably six or more characters, that should be known only to the accessor. Passwords and log-on codes should have an expiration feature, should not be reusable, should provide for secrecy (e.g., non-print, non-display feature, encryption), and should limit the number of unsuccessful access attempts. Passwords should conform to a set of rules established by management.

In addition to the password weaknesses cited earlier in Section 3.4.3, passwords can be misused. For example, someone who can electronically monitor (or eavesdrop on) the channel may also be able to "read" or identify a password and later impersonate the sender. Popular computer network media such as Ethernet or token rings are vulnerable to such abuses. Encryption authentication schemes can overcome such problems.

o Something possessed by an individual: such as a magnetically encoded card (e.g., smart cards) or a key for a lock. Techniques such as encryption may be used in connection with card devices to further enhance their security.

Dial back is a combination method where users dial in and identify themselves in a prearranged method. The system then breaks the connection and dials the users back at a predetermined number. There are also devices to determine, without the call back, that a remote device hooked to the computer is actually an authorized device.

Other security devices, at the point of logon and validation devices on the LAN server,

include port-protection devices and random number generators.

o Something about the individual: these include biometric techniques that measure some

physical attribute of a person (e.g., fingerprints, voiceprints, signatures, or retinal patterns) and transmit the information to the system that is authenticating the person. Cost is a major factor for these techniques.

Authorization/Access Controls. These are hardware or software features used to detect and/or permit only authorized access to or within the system (e.g., the use of access lists). Authorization/access

controls include controls to restrict access to the operating system and programming resources, limits on access to associated applications, and controls to support security policies on network and internetwork access.

In general, authorization/access controls are the means whereby management or users determine:

o who will have

o what modes of access to

o which objects and resources

The who may include not only people and groups but also individual PCs and even modules within an application. The modes of access typically include read, write, and execute access to data, programs, servers, and internetwork devices. The objects that are candidates for authorization control include: data objects (directories, files, libraries, etc.), executable objects (commands, programs, etc.), input/output devices (printers, tape backups), transactions, control data within the applications, named groups of any of the foregoing elements, and the servers and internetwork devices.

Integrity Controls. Integrity controls are used to protect the operating system, applications, and information in the system from accidental or malicious alteration or destruction, and provide assurance

to users that data have not been altered (e.g., message authentication). Integrity starts with the identification of those elements that require specific integrity controls:

· The foundations of integrity controls are the identification/authentication and authorization/access controls. These controls include careful selection of and adherence to vendor-supplied LAN administrative and security controls. Additionally, the use of software packages to automatically check for viruses is effective for integrity control.

· Data integrity includes two mechanisms that are at the heart of fraud and error control: the well-formed transaction and segregation of duties among employees. A well-formed

· transaction has a specific, constrained, and validated set of steps (and programs) for handling data with automatic logging of all data modifications so that actions can be audited later. The most basic segregation of duty rule is that a person creating or certifying a well-formed transaction may not be permitted to execute it.

· Two cryptographic techniques provide integrity controls for highly sensitive information:

1. - Message Authentication Codes (MACs) are a type of cryptographic checksum that can protect against unauthorized data modification, both accidental and intentional. See FIPS PUB 113, Computer Data Authentication, May 20, 1985 and NBS Special Publication 500-156, Message Authentication Code (MAC) Validation System: Requirements and Procedures, May 1988.

2. - Digital signatures authenticate the integrity of the data and the identity of the author. NIST is in the process of issuing a Digital Signature Standard that is intended for use in electronic mail, electronic funds transfer, electronic data interchange, software distribution, data storage, and other applications that require data integrity assurance and sender authentication.

Audit Trail Mechanisms. Audit controls provide a system monitoring and recording capability to retain

or reconstruct a chronological record of system activities (e.g., system log files). These audits records help to establish accountability when something happens or is discovered. Audit controls should be implemented as part of a planned LAN security program. LANs have varying audit capabilities, which include:

· Exception logs record information relating to system anomalies such as unsuccessful password or logon attempts, unauthorized transaction attempts, PC/remote dial-in lockouts, and related matters. Exception logs should be reviewed and retained for specified periods.

· Event records identify transactions entering or exiting the system, and journal tapes are a backup of the daily activities.

Confidentiality Controls. These controls provide protection for data that must be held in confidence and protected from unauthorized disclosure. The controls may provide data protection at the user site, at a computer facility, in transit, or some combination of these (e.g., encryption).

· Confidentiality relies on the totality of LAN security (similar to integrity), and additional protection may include encryption.

· Encryption is a means of encoding (scrambling) data so that they are unreadable. When the data are received, the reverse scrambling takes place. The scrambling and descrambling requires an encryption capability at either end and a specific key, either hardware or software to code and decode the data. Encryption allows only authorized users to have access to applications and data. The NIST-sponsored Data Encryption Standard (DES) "is mandatory for all Federal agencies, including defense agencies, for the protection of sensitive unclassified information when the agency or department determines that cryptographic protection is required."

· The use of cryptography to protect user data from source to destination (end-to-end encryption) is a powerful tool for providing network security. This form of encryption is typically applied at the transport layer of the network (layer 4). End-to-end encryption cannot be employed (to maximum effectiveness) if application gateways are used along the path between communicating entities. These gateways must, by definition, be able to access protocols at the application layer (layer 7), above the layer at which the encryption is employed. Hence the user data must be decrypted for processing at the application gateway and then re-encrypted for transmission to the destination (or another gateway). In such an event the encryption being performed is not really end-to-end.

· There are a variety of low-cost, commercial security/encryption products available that may provide adequate protection for unclassified use, some with little or no maintenance of keys. Many commercial software products have security features that may include encryption capabilities, but do not meet the NIST-required encryption standards. WordPerfect is an example of a product that automatically encrypts files when they are password protected (and the encrypted files can be stored on diskettes), but the encryption does not meet the requirements of the DES.

3.5.3 Operational Safeguards

Operation safeguards are the day-to-day procedures and mechanisms to protect LANs, as basically defined in OMB Bulletin 90-08. These safeguards include:

Backup and Contingency Planning. The goal of an effective backup strategy is to minimize the number

of workdays that can be lost in the event of a disaster (e.g., disk crash, virus, fire). A backup strategy should indicate:

· the type/scope of backup: complete system backups, incremental system backups (changes), file/data backups, and even dual backup disks (disk "mirroring").

· the frequency of the backups: AM/PM, nightly, weekly, monthly.

· the time period for which the backup copies are kept: daily backups may be kept for a week, weekly backups may be kept for a month, monthly backups may be kept for a year.


Contingency/Disaster Recovery Planning consists of workable procedures for continuing to perform essential functions in the event that information technology support is interrupted. Application plans should be coordinated with the back-up and recovery plans of any installations and networks used by the application. Appendix E contains a sample contingency plan. Appropriate emergency, backup and contingency plans and procedures should be in place and tested regularly to assure the continuity of support in the event of system failure. These plans should be known to users and coordinated with them.

Offsite storage of critical data, programs, and documentation is important. In the event of a major

disaster such as fire, or even extensive water damage, backups at offsite storage facilities may be the only way to recover important data, software, and documentation. Offsite storage is a mandatory requirement for Level 2 and 3 (and 4) protection requirements.

Physical and Environmental Protection. These are controls used to protect against a wide variety of physical and environmental threats and hazards, including deliberate intrusion, fire, natural hazards, and utility outages or breakdowns. Several areas come within the direct purview of the LAN/security staff, including: adequate surge protection, battery/backup power, room/cabinet locks, and possibly additional air conditioning. Surge protection and backup power will be discussed in more detail.

Surge suppressors that protect stand-alone equipment may actually cause damage to computers and other peripherals in a network. Ordinary surge protectors and uninterruptible power supplies (UPS) can

actually divert dangerous electrical surges into network data lines and damage equipment connected to that network. Power surges are momentary increases in voltage, up to 6,000 volts in 110 volt power systems, making them dangerous to delicate electronic components and data as they search for paths to ground. Ordinary surge protectors simply divert surges from the hot line to the neutral and ground wires, where they are assumed to flow harmlessly to earth. The extract below summarizes this surge protection problem for networks:

Computers interconnected by datalines present a whole new problem because network (and modem) datalines use the powerline ground circuit for signal voltage reference. When a conventional surge protector diverts a surge to ground, the surge directly enters the datalines through the ground reference. As [NIST's Francois] Martzloff explained in "Protecting Computer Systems Against Power Transients," this causes high surge voltages to appear across datalines between computers, and dangerous surge currents to flow in these datalines. Data Communications reported in December 1990 that "Most experts now agree that TVSSs (Transient Voltage Surge Suppressors) based on conventional diversion designs should not be used for networked equipment." LAN Times commented in May 1990 "Surge protectors may contribute to LAN crashes by diverting surge pulses to ground thereby contaminating the reference used by data cabling." This problem was first discovered by a team of NIST researchers led by Martzloff in 1988. To avoid having the ground wire act as a "back door" entry for surges to harm a computer's low-voltage circuitry, network managers should consider power-line protection that:

· Provides low let-through voltage (under 250 volts peak is harmless).

· Does not use the safety ground as a surge sink and preserves it for its role as voltage reference.

· Attentuates the fast rise times of all surges, to avoid stray coupling into computer circuitry.

· Intercepts all surge frequencies, including internally generated high-frequency surges.

The use of an UPS for battery/backup power can make the difference between a "hard or soft crash." "Hard crashes" are the sudden loss of power and the concurrent loss of the system, including all data and work-in-progress in the servers' random-access-memory (RAM). An UPS provides immediate backup power to permit an orderly shutdown or "soft crash" of the LAN, thus saving the data and work-inprogress. The UPS protecting the server should include software to alert the entire network of an imminent shutdown, permitting users to save their data. LAN servers should be protected by UPSes, and UPS surge protectors should avoid the "back door" entry problems described above.

Production and Input/Output Controls. These are controls over the proper handling, processing, storage, and disposal of input and output data and media, including: locked storage of sensitive paper and electronic media, and proper disposal of materials (i.e., erasing/degaussing diskettes/tape and shredding sensitive paper material).

Audit and Variance Detection. These controls allow management to conduct an independent review of system records and activities in order to test for adequacy of system controls, and to detect and react to departures from established policies, rules, and procedures. Variance detection includes the use of system logs and audit trails to check for anomalies in the number of system accesses, types of accesses, or files accessed by users.

Hardware and System Software Maintenance Controls. These controls are used to monitor the installation of and updates to hardware and operating system and other system software to ensure that the software functions as expected and that an historical record is maintained of system changes. They may also be used to ensure that only authorized software is allowed on the system. These controls may include hardware and system software configuration policy that grants managerial approval to modifications, then documents the changes. They may also include virus protection products.

Documentation. These documentation controls are in the form of descriptions of the hardware, software, and policies, standards, and procedures related to LAN security, to include vendor manuals, LAN procedural guidance, and contingency plans for emergency situations. They may also include network diagrams to depict all interconnected LANs/WANs and the safeguards in effect on the network devices.

3.5.4 Virus Safeguards

Virus safeguards include good security practices cited above (e.g., backups, use of only agency approved software, testing of new software). The DHHS AISSP Handbook requires an OPDIV virus prevention

and protection program, including the designation and training of a computer virus specialist (and backup). Each LAN should be part of this program. More stringent policies should be considered, as needed, such as:

· Use of anti-virus software to prevent, detect, and eradicate viruses

· Use of access controls to more carefully limit users

· Review of the security of other LANs before connecting

· Limiting of electronic mail to non-executable files

· Use of call-back systems for dial-in lines


Additionally, "Five common-sense tips for safer computing" are provided below:

· If the software allows it, apply write-protect tabs to all program disks before installing new software. If it does not, write protect the disks immediately after installation.

· Do not install software without knowing where it has been.

· Make executable files read-only. It won't prevent virus infections, but it can help contain those that attack executable files (e.g., files that end in ".exe" or ".com"). Designating executable files as read-only is easier and more effective on a network, where system managers control read/write access to files.

· Abolish "SneakerNet." Boot sector viruses are especially pernicious. The most common virus, "Stoned," travels in the boot sector of floppy disks, which are passed from user to user and PC to PC. If an infected floppy disk is left in the A: drive and the user turns on the PC, the virus will spread to the hard disk as quickly as the "non-system disk" error appears onscreen. Transferring data files via networks, E-mail, or direct modem connections will minimize the possibility of spreading boot sector viruses.

· Back-up files. The only way to be sure the files will be around tomorrow is to back them up today.


3.6.1 Formal versus Informal

OMB Circular No. A-130 states that methodologies may range from informal reviews of small office automation installations through formal risk assessments at major data centers. An informal security review can be used for systems with Level 1 security designations. Formal risk assessments are required for Level 2 and 3, in accordance with the DHHS AISSP Handbook. See Section 4 below for further discussion of levels of protection.

3.6.2 Automated Risk Assessment

There are a considerable number of automated risk assessment packages, of varying capabilities and costs, available in the market place. These automated packages address large and medium facilities, applications, office automation, and even LANs to some extent. Regrettably, there appears to be no automated package that adequately addresses LANs. Several packages contain general analyses of

network vulnerabilities applicable in part to LANs, and many PC assessment protocols include questions relating to LAN attachments. However, to date no package has been found to have adequate coverage of LAN administration, protection of file servers, and PC/LAN backup practices and procedures.

3.6.3 Questionnaires and Checklists

The key to good security management is measurement - knowing where one is in relation to what needs to be done.

Questionnaires are one way to gather relevant information from the user community. A PC/LAN

Questionnaire can be a simple, quick, and effective tool to support informal and formal risk assessments. For small, informal risk assessments, the PC/LAN Questionnaire can be the main assessment tool. A checklist is another valuable tool for helping to evaluate the status of security. Section 4 discusses the use of questionnaires and checklists and two samples are included in the appendices.

A customized, DHHS version of an automated questionnaire and assessment package is being made

available to the Department. This PC-based product, MicroSecure Self Assessment from Boden

Associates, prompts the user to respond to a series of PC and LAN questions, which are tailored on-line to the user's environment, and then provides recommendations to improve the user's security practices

and safeguards. Designed for the average PC user, the product functions as a risk assessment tool.

A questionnaire/checklist may be a useful first step in determining if a more formal/extensive risk assessment needs to be done, as well as to guide the direction of the risk assessment.


This section provides a step-by-step approach for implementing cost-effective LAN security.


The first step in LAN security implementation is to know who is responsible for doing what. LAN security is a complex undertaking, requiring an integrated team effort. Chapter 1 of the AISSP Handbook cites responsibilities for Departmental security, including:

· Managers of AIS Facilities and Information Technology Utilities (ITUs) (which include LAN/WANs)

· Managers of AISs and Application Systems (which run on LANs)

In addition to the AISSP Handbook requirements, every area network requires a LAN/WAN

Administrator and an Information Systems Security Officer (ISSO) whose specific duties include the implementation of appropriate general, technical (e.g., access controls and internetwork security), and operational controls (e.g., backups and contingency planning). In general, the ISSO is responsible for the development and coordination of LAN security requirements, including the Computer Systems

Security Plan. The LAN Administrator is responsible for the proper implementation and operation of security features on the LAN.


The second step is to understand the type and relative importance of protection needed for a LAN. 4.2.1Protection Objectives

As stated in Section 3, a LAN may need protection for reasons of confidentiality, integrity, and availability. For each of the three categories there are three subcategories to determine the level of security needed: High, Medium, or Low.

Rank the security objectives for the LAN being reviewed, using the following matrix:

Table 4-1: Security Objectives and Levels



Level of Protection Needed


(Level 3)


(Level 2)


(Level 1)




The result is an overall security designation of low (Level 1), medium (Level 2), or high (Level 3). In all instances, the security level designation of a LAN should be equal to or higher than the highest security level designation of any data it processes or systems it runs.

This security level designation determines the minimum security safeguards required to protect sensitive data files and to ensure the operational continuity of critical processing capabilities. Please refer to the DHHS AISSP Handbook, Chapter II, Security Level Designations for additional details.

4.2.2 DHHS Security Level Requirements

The following minimum security requirements have been extracted from the DHHS AISSP Handbook,

Chapter III, Security Level Requirements:

Level 1 Requirements: The controls required to adequately safeguard a Level 1 system are

considered good management practices. These include, but are not limited to:

a. AIS security awareness and training

b. Position sensitivity designations.

c. Physical access controls.

d. A complete set of AIS documentation.

Level 2 Requirements: The controls required to adequately safeguard a Level 2 system include all of the requirements for a Level 1, plus the following requirements:

a. A detailed risk management program (to be included in the AISSP).

b. Record retention procedures.

c. A list of authorized users.

d. Security review and certification procedures.

e. Clearance (i.e., appropriate background checks) for persons in sensitive positions, and for all contractor personnel supporting sensitive systems.

f. A detailed fire/catastrophe plan.

g. A formal written contingency plan. h. A formal risk analysis.

i. An automated audit trail.

j. Authorized access and control procedures. k. Secure physical transportation procedures. l. Secure telecommunications.

m. An emergency power program.

Level 3 Requirements: The controls required to adequately safeguard a Level 3 system include

all of the requirements for Levels 1 and 2, plus the following:

a. More secure data transfer, maybe including encryption.

b. Additional audit controls.

c. Additional fire prevention requirements.

d. Provision of waterproof covers for computer equipment.

e. Maintenance of a listing of critical-sensitive clearances.

There is also a set of Level 4 Requirements for classified information that comes under National Security policies. No Level 4 information should be stored, processed, or transmitted on an DHHS LAN.

4.2.3 Sample Table of Mandatory/Optional Safeguards

The following table provides a quick (but not exhaustive) summary of mandatory and optional safeguards for Level 2 LANs. This list summarizes requirements cited in the DHHS AISSP Handbook, Exhibit

III-A: Matrix of Minimum Security Safeguards.

Table 4-2: Examples of Mandatory/Optional Safeguards

(Level 2 protection of LANs)




1.General Safeguards:

Security officer


Security training


Screen personnel


Risk analysis


2.Technical Safeguards:



Limit log-on attempts


Access rights lists/profiles




Message authentication


Audit trail mechanisms




3.Operational Safeguards:



Contingency plan


Offsite storage


Audit and variance detection


Maintenance controls


Physical/environmental controls


Handling/storage controls




Virus prevention measures


4.2.4 Determine Detailed Security Protections

Table 4-2 is still general. Specific, detailed security protections must be determined, starting with who gets what access, and when. Management, LAN, and security officials, working with key users, must determine the detailed security protections. Procedures for maintaining these protections must be formalized (e.g., who reviews audit logs; who notifies LAN administrator of departed personnel).


4.3.1 Role of the PC/LAN Questionnaire

Security programs require the gathering of a considerable amount of information from managers,

technical staff, and users. Interviews are one way, and these are often used with technical staff. Another way to obtain information is with a PC questionnaire, which is a particularly good method for reaching

a reasonable segment of the user community, quickly and efficiently. With minor updating, these surveys can be used periodically to provide a current picture of the security environment.

We recommend using a PC/LAN questionnaire for Level 1 reviews and to support Level 2 and 3 risk assessments. In other words, a questionnaire can be the focus of an informal risk assessment and can be a major element in a formal risk assessment. A PC/LAN questionnaire, for example, can collect the following types of information to help:

· Identify applications and general purpose systems.

· Identify sensitivity and criticality

· Determine specific additional security needs, relating to:

1. -Security Training

2. -Access controls

3. -Backup and recovery requirements

4. -Input/output controls

5. -And many other aspects of security


Appendix C contains a sample PC/LAN questionnaire to illustrate this methodology. This questionnaire can be passed out to a representative sampling of PC users (e.g., novices to experienced), asking them to take 15-20 minutes to fill out the form. The aggregated results of this questionnaire should provide a reasonable number of indicators to assess the general status of PC computing practices within the LAN/WAN environment.

4.3.2 Role of the Computer System Security Plan

Develop a Computer Systems Security Plan (CSSP) for Level 2 and Level 3 LANs and WANs. CSSPs

are currently outlined in OMB Bulletin No. 90-08 and are an effective tool for organizing LAN security. The CSSP format provides simplicity, uniformity, consistency, and scalability. The CSSP is to be used

as the risk management plan for controlling all recurring requirements, including risk updates, personnel screening,training, etc. Note that a Computer Security Act CSSP is not necessarily required for all Level 2 LANs and WANs.

See Appendix D, Sample Security Plan, for an example of a LAN Computer System Security Plan.

See Appendix F, LAN/WAN Security Plan Checklist, for a method to review security plans for

compliance with OMB guidance.

4.3.3 Risk Assessment

As required by the AISSP Handbook, risk assessments include: identification of informational and other

assets of the system; threats that could affect the confidentiality, integrity, or availability of the system; system vulnerabilities/susceptibility to the threats; potential impacts from threat activity; identification of protection requirements to control the risks; and selection of appropriate security measures.

Risk assessment for general purpose systems, including LANs/WANs, are required at least every five

years, or more often when there are major operational, software, hardware, or configuration changes. Section 3, "Risk Assessments", may be used as a guide for the risk assessment process. See also appropriate NIST publications (e.g., FIPS PUB 65, Guideline for Automatic Data Processing Risk


4.3.4 The Contingency Plan

In view of the importance of contingency planning, Appendix E contains a sample Contingency Plan that can be amplified and tailored to specific LANs. This sample plan follows the requirements of the DHHS AISSP Handbook, OMB Circular No. A-130, and FIPS PUB 87, Guidelines for ADP Contingency

Planning, March 1981. For additional guidance, see also: Information Technology Installation Security, Federal Systems Integration and Management Center (FEDSIM), GSA, December 1988.

4.3.5 An Annual Review & Training Session

An ideal approach would be to conduct a yearly LAN meeting where LAN management, security, and end-user personnel can get together and review the security of the system. LAN meetings are an ideal way to satisfy both the security needs/updates of the system and the training/orientation needs of the individuals who are associated with the system. The process can be as simple as reviewing the CSSP,

item by item, for additions, changes, and deletions. General discussion on special security topics such as planned network changes and OPDIV management concerns can round out the agenda. A summary

of the meeting is useful for personnel who were unable to attend, for managers, and for updating the management plan.

An often overlooked fact is that "LAN security" is only as good as the security being practiced. Information and system security is dependent on each user. Users need to be sensitized, trained, and monitored to ensure good security practices.

4.3.6 Update Management/Budget Plan

The management/budget plan is the mechanism for getting review and approval of security requirements in terms of specific projects, descriptions, responsibilities, schedule, and costs. This plan should be updated yearly to reflect the annual review findings.


Accreditation. The authorization and approval, granted to an ADP system or network to process sensitive data in an operational environmental, and made on the basis of a certification by designated technical personnel of the extent to which design and implementation of the system meet prespecified technical requirements for achieving adequate data security. 1,2

Application System. An application system is a software package that processes, transmits, or disseminates information according to established internal procedures. An application system is run at an automated information system facility. A word processor usually runs only one application system. A mainframe computer may run thousands of application systems. 3

Automated Information System (AIS). An AIS is the organized collection, processing, transmission, and dissemination of information in accordance with defined procedures. 2,3,4

Automated Information System (AIS) Facility. An AIS facility is an organizationally defined set of personnel, hardware, software, and physical facilities, a primary function of which is the operation of an automated information system(s) and an application system(s). AIS facilities range from large centralized computer centers to individual stand-alone microprocessors such as personal computers and word processors. 3

Certification. A technical evaluation made as part of and in support of the accreditation process, that establishes the extent to which a particular computer system or network design and implementation meet a prespecified set of security requirements. 1,2

Computer Security. Computer Security is the protection of a computer system against internal failures, human errors, attacks, and natural catastrophes that might cause improper disclosure, modification, destruction, or denial of service. 1,2

Computer System Security Plan (CSSP). This plan is a document describing the security and privacy requirements of a given system and the agency's plan to meet these requirements. 2,5

Information Technology Utility (ITU). An ITU is an organizationally defined set of personnel,

hardware, software, and physical facilities, a primary function of which is to coordinate the operation of geographically dispersed automated information systems and automated information system facilities. ITUs range in size from wide area networks covering widely dispersed geographical areas to local area networks covering a single office. 3

Local Area Network (LAN). A data network, located on a user's premises, within a limited geographic region. Communication within a local area network is not subject to external regulation; however, communication across the network boundary may be subject to some form of regulation. 6

Personnel Security. Personnel security refers to a program that determines the sensitivity of positions

and screens individuals who participate in the design, operation, or maintenance of automated information systems or who have access to such systems. 3

Physical Security. Physical security refers to the combination of devices that bar, detect, monitor, restrict, or otherwise control access to sensitive areas. Physical security also refers to the measures to protect a facility that houses AIS assets and its contents from damage by accident, malicious intent, fire, loss of utilities, environmental hazards, and unauthorized access. 3

Sensitive Information. Sensitive information is any information, the loss, misuse, disclosure, or unauthorized access to or modification of which could adversely affect the national interest or the conduct of Federal programs, or the privacy to which individuals are entitled under section 552a of Title 5, United States Code (the Privacy Act), but which has not been specifically authorized under criteria established by an Executive Order or an Act of Congress to be kept secret in the interest of national defense or foreign policy. 2,3,7

Wide Area Network (WAN). A WAN is an arrangement of data transmission facilities that provides communications capability across a broad geographic area (e.g., DIMES).


1 FIPS Pub 102, Guideline for Computer Security Certification and Accreditation, September 1983.

2 DHHS IRM Circular # 10, "Automated Information Systems Security Program," September 30, 1991

3 DHHS Automated Information Systems Security Program Handbook, February 1, 1991

4 OMB Circular No. A-130, Management of Federal Information Resources, Appendix III, "Security of Federal Automated Information Systems," December 12, 1985.

5 OMB Bulletin No. 90-08, "Guidance for the Preparation of Security Plans for Federal Computer Systems that Contain Sensitive Information," July 9, 1990.

6 FIPS PUB 11-3, Dictionary for Information Systems, 1991 (ANSI X3.172-1990)

7 Computer Security Act of 1987, January 8, 1988, P.L. 100-235


"Federal Legislation, Regulations, Standards, and Guidelines"