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 kernel's path lookup logic allows that user to escape the jail's 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 jail's filesystem root.
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Freebsd | — | Upgrade FreeBSD | Jan 28, 2026 | Jan 28, 2026 |
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