CVE-2026-72034 fhandle: reject detached mounts in capable_wrt_mount()
A race condition in the Linux kernel fhandle subsystem can cause a null pointer dereference and system panic when handling detached mounts.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72034?
CVE-2026-72034 is a high-severity vulnerability in Linux, published on 15 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
fhandle: reject detached mounts in capable_wrt_mount()
The recent fhandle RCU fix moved the mount namespace capability check into capable_wrt_mount(), so a non-NULL mnt_namespace survives the ns_capable() dereference. The helper still assumes the later READ_ONCE(mount->mnt_ns) must be non-NULL because may_decode_fh() checked is_mounted() first.
That assumption is not stable. A detached mount from open_tree(..., OPEN_TREE_CLONE) can be dissolved on fput while open_by_handle_at() is between those checks, and umount_tree() can clear mount->mnt_ns. If the helper observes NULL, it dereferences mnt_ns->user_ns and panics.
Return false when the RCU read observes a detached mount. This keeps the relaxed permission path conservative: a mount no longer attached to a namespace cannot authorize open_by_handle_at() access.
Weakness: CWE-476
Which versions are affected by CVE-2026-72034?
How do I fix CVE-2026-72034?
Apply the vendor's patch.
Is CVE-2026-72034 being exploited?
There is no known exploitation of CVE-2026-72034 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72034, DEBIAN-CVE-2026-72034, GHSA-g7v4-chcg-vj96, UBUNTU-CVE-2026-72034.