AppArmor Breakout: Profile Vulnerability

TL;DR

The provided AppArmor profile has a vulnerability allowing an attacker to potentially break out of the jail by exploiting the ability to execute programs in /usr/bin. Specifically, the profile allows execution of any program within /usr/bin, which could include utilities like sudo or other privilege escalation tools if they exist there.

Solution Guide

1. Understand the Vulnerability: The core issue is overly permissive access to /usr/bin. AppArmor profiles should restrict execution to only *necessary* binaries, not entire directories. Allowing all programs in /usr/bin opens a significant attack surface.
2. Identify the Profile: Locate the specific AppArmor profile being used. This usually involves checking system logs or configuration files. The exact location varies depending on your distribution (e.g., /etc/apparmor.d/).
3. Review the Profile Contents: Examine the profile file to confirm the problematic rule allowing access to /usr/bin. Look for lines similar to:

   /usr/bin/* ixr

   This grants execute permissions (ixr) to all files within /usr/bin.

4. Restrict Executable Access: Modify the profile to only allow execution of *required* binaries in /usr/bin. For example, if the application needs to run ls and cat:

   /usr/bin/ls ixr

   /usr/bin/cat ixr

5. Consider Using Specific Paths: Instead of relying on /usr/bin, if possible, move the required executables to a dedicated directory owned by the application and restrict access to that directory only.

   /opt/app_exec/* ixr

6. Audit Profile Rules: Regularly audit AppArmor profiles for overly permissive rules. Tools like aa-audit can help identify potential issues:

   sudo aa-audit -l /path/to/profile

7. Reload the Profile: After making changes, reload the AppArmor profile to apply them.

   sudo apparmor_parser -r /path/to/profile

8. Test the Changes: Thoroughly test the application after reloading the profile to ensure it still functions correctly and that the breakout vulnerability is mitigated. Attempt to execute unintended binaries from within the AppArmor jail.
   • Try running sudo (if present in /usr/bin) from within the jailed environment.
   • Attempt to access other system utilities.