CVE-2026-52973 futex: Drop CLONE_THREAD requirement for private default hash alloc
A use-after-free in the Linux kernel futex subsystem allows attackers to potentially execute code or escalate privileges via specific clone operations.
- 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-2026-52973?
CVE-2026-52973 is a high-severity use after free vulnerability in Linux kernel, published on 24 Jun 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: Drop CLONE_THREAD requirement for private default hash alloc
Currently need_futex_hash_allocate_default() depends on strict pthread semantics, abusing CLONE_THREAD. This breaks the non-concurrency assumptions when doing the mm->futex_ref pcpu allocations, leading to bugs[0] when sharing the mm in other ways; ie:
BUG: KASAN: slab-use-after-free in futex_hash_put
... where the +1 bias can end up on a percpu counter that mm->futex_ref no longer points at.
Loosen the check to cover any CLONE_VM clone, except vfork(). Excluding vfork keeps the existing paths untouched (no overhead), and we can't race in the first place: either the parent is suspended and the child runs alone, or mm->futex_ref is already allocated from an earlier CLONE_VM.
Which versions are affected by CVE-2026-52973?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-52973?
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-2026-52973 being exploited?
There is no known exploitation of CVE-2026-52973 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-52973, DEBIAN-CVE-2026-52973, GHSA-9qj4-wr4g-7m6f, UBUNTU-CVE-2026-52973.