S 4.40 Preventing unauthorised use of computer microphones

Initiation responsibility: IT Security Management

Implementation responsibility: IT-users

The microphone on a networked computer can be used by persons having access to the corresponding device file (e.g. /dev/audio under UNIX). Under Windows NT the access rights defined in the appropriate Registry key ( HKEY_LOCAL_MACHINE\HARDWARE \) determine who can activate the computer microphone. These permissions must therefore be granted judiciously. Access to the device should only be possible whilst somebody is working on the IT system. If a microphone is to be prevented from being used in general, it must, if possible, be switched off or separated physically from the computer.

If the microphone is integrated into the computer and can only be activated/deactivated using software, the access rights must be set so that no unauthorised user can use it. Under UNIX this is possible, for example, by depriving all users of the right to read the /dev/audio device file; under Windows NT by depriving users of access to the appropriate Registry keys. This prevents normal users from using the microphone but still allows them to play back audio files.

On IT systems equipped with a microphone, a check must be made as to whether access rights and ownership are changed when the device is accessed. If this is the case, or if it is desirable that every user should be able to use the microphone without the Administrator having to release it individually, the Administrator must provide a command which

• can only be activated once a user has logged on to the IT system

• can only be activated by this user and

• withdraws the access rights from this user after log-out.

If access to the microphone is not controlled by means of a secure command, the microphone must be disconnected physically from the computer or the computer must be taken off the network.

Computers with built-in microphones should be removed from the room during confidential discussions or at least be switched off. In the case of a laptop, any non-essential connections to communications networks, for example ISDN, should be disconnected. In most cases the simplest way of achieving this is to pull out the relevant cable.

Additional controls:

• Can the computer's microphone be switched off or disconnected physically from the computer?

• Who has access to the microphone's device file or to the entries in the Registry where hardware settings may be manipulated?