Practical UNIX and Internet Security, 3rd Edition

Modems and Security

Modems raise a number of security concerns because they create links between your computer and the outside world. Modems can be used by individuals inside your organization to remove confidential information. Modems can be used by people outside your organization to gain unauthorized access to your computer. If your modems can be reprogrammed or otherwise subverted, they can be used to trick your users into revealing their passwords. And, finally, an attacker can eavesdrop on a modem communication.

Despite the rise of the Internet, modems remain a popular tool for breaking into large corporate networks. The reason is simple: while corporations closely monitor their network connections, modems are largely unguarded and unaudited. In many organizations, it is difficult and expensive to prevent users from putting modems on their desktop computers and running “remote access” software. This happens much more frequently than you might expect.

So what can be done? To maximize security, modems should be provided by the organization and administered in a secure fashion.

The first step is to protect the modems themselves. Be sure they are located in a physically secure location, so that no unauthorized individual can access them. The purpose of this protection is to prevent the modems from being altered or rewired. Some modems can have altered microcode or passwords loaded into them by someone with appropriate access, and you want to prevent such occurrences. You might make ...