CVE-2025-39976 futex: Use correct exit on failure from futex_hash_allocate_default()
Incorrect error handling in Linux kernel futex allocation can cause a crash by unlocking unheld locks, leading to 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-2025-39976?
CVE-2025-39976 is a high-severity vulnerability in Linux, published on 15 Oct 2025. 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: Use correct exit on failure from futex_hash_allocate_default()
copy_process() uses the wrong error exit path from futex_hash_allocate_default(). After exiting from futex_hash_allocate_default(), neither tasklist_lock nor siglock has been acquired. The exit label bad_fork_core_free unlocks both of these locks which is wrong.
The next exit label, bad_fork_cancel_cgroup, is the correct exit. sched_cgroup_fork() did not allocate any resources that need to freed.
Use bad_fork_cancel_cgroup on error exit from futex_hash_allocate_default().
Which versions are affected by CVE-2025-39976?
How do I fix CVE-2025-39976?
Apply the vendor's patch.
Is CVE-2025-39976 being exploited?
There is no known exploitation of CVE-2025-39976 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-39976, DEBIAN-CVE-2025-39976, GHSA-rgc5-qvp4-69x6, UBUNTU-CVE-2025-39976.