42.0 Confining Privileges with AppArmor

Many security vulnerabilities result from bugs in trusted programs. A trusted program runs with privilege that some attacker would like to have. The program fails to keep that trust if there is a bug in the program that allows the attacker to acquire that privilege.

Novell® AppArmor is an application security solution designed specifically to provide least privilege confinement to suspect programs. AppArmor allows the administrator to specify the domain of activities the program can perform by developing a security profile for that application—a listing of files that the program may access and the operations the program may perform.

Effective hardening of a computer system requires minimizing the number of programs that mediate privilege then securing the programs as much as possible. With Novell AppArmor, you only need to profile the programs that are exposed to attack in your environment, which drastically reduces the amount of work required to harden your computer. AppArmor profiles enforce policies to make sure that programs do what they are supposed to do, but nothing else.

Administrators only need to care about the applications that are vulnerable to attacks and generate profiles for these. Hardening a system thus comes down to building and maintaining the AppArmor profile set and monitoring any policy violations or exceptions logged by AppArmor's reporting facility.

Building AppArmor profiles to confine an application is very straightforward and intuitive. AppArmor ships with several tools that assist in profile creation. It does not require you to do any programming or script handling. The only task that is required from the administrator is to determine a policy of strictest access and execute permissions for each application that needs to be hardened.

Updates or modifications to the application profiles are only required if the software configuration or the desired range of activities changes. AppArmor offers intuitive tools to handle profile updates or modifications.

Users should not notice AppArmor at all. It runs behind the scenes and does not require any user interaction. Performance is not affected noticeably by AppArmor. If some activity of the application is not covered by an AppArmor profile or if some activity of the application is prevented by AppArmor, the administrator needs to adjust the profile of this application to cover this kind of behavior.

This guide outlines the basic tasks that need to be performed with AppArmor to effectively harden a system. For more in-depth information, refer to Novell AppArmor 2.0 Administration Guide.