By default, jailed processes cannot mount filesystems, including nullfs(4). However, the allow.mount.nullfs option enables mounting nullfs filesystems, subject to privilege checks.
If a privileged user within a jail is able to nullfs-mount directories, a limitation of the kernels path lookup logic allows that user to escape the jails chroot, yielding access to the full filesystem of the host or parent jail.
In a jail configured to allow nullfs(4) mounts from within the jail, the jailed root user can escape the jails filesystem root.
Weakness
The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.
Potential Mitigations
Related Attack Patterns
- https://cwe.mitre.org/data/definitions/122.html
- https://cwe.mitre.org/data/definitions/233.html
- https://cwe.mitre.org/data/definitions/58.html