Modem phone lines are not restricted and configured to their mission required purpose (i.e. inward/outward dial only).

Requirement: The IAO will ensure that all modem phone lines are restricted and configured to their mission required purpose (inward dial only or outward dial only).

Ubiquitous phone lines open major security holes in a network. The more tightly they can be controlled, the less the exposure to vulnerabilities. Allowing special features to remain active on modem phone lines create advantageous situations for malicious attacks. An attacker may use special features to forward modem or voice calls to destinations that cause toll-fraud, or forward the number to itself causing a denial of service. Telephone lines that provide DSN modems dial tone will be provisioned only with their required functions. Some components of the DSN "dial back" option may require two modems for proper operation. If a modem is dedicated to receive calls, it should be provisioned to not allow outbound calling. If a modem is dedicated to place calls, it should be provisioned to not accept incoming calls.