CVE-2026-80778 futex/pi: Reject cross-mm private futex owners
A use-after-free in the Linux kernel futex subsystem allows local attackers to escalate privileges or cause a denial of service.
- 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-2026-80778?
CVE-2026-80778 is an use after free vulnerability in Linux, published on 4 Sep 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:
futex/pi: Reject cross-mm private futex owners
A private futex key borrows the waiter's mm without taking an mm_users reference. Nevertheless, attach_to_pi_owner() currently accepts an owner from a different address space and copies the private key into the owner's PI state.
When that owner exits, exit_pi_state_list() uses the saved key to find the hash bucket and acquires a reference to the waiter's private hash. If the last user of the waiter's mm exits concurrently, futex_hash_free() frees the hash while the owner still uses its bucket and reference.
Prevent this by validating in attach_to_pi_owner() that, for private futexes, the owner mm and waiter mm are the same. Perform the check with the owner's pi_lock held and after validating owner::futex::state to serialize against a concurrent PI-state exit cleanup.
[ tglx: Amended comment ]
Which versions are affected by CVE-2026-80778?
How do I fix CVE-2026-80778?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-80778 being exploited?
There is no known exploitation of CVE-2026-80778 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-80778, DEBIAN-CVE-2026-80778, GHSA-pwhw-9cfc-qqqx, UBUNTU-CVE-2026-80778.