CVE-2025-40348 slab: Avoid race on slab->obj_exts in alloc_slab_obj_exts
A race condition in the Linux kernel slab allocator can lead to a NULL pointer dereference and system crash.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40348?
CVE-2025-40348 is a vulnerability in Linux, published on 16 Dec 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:
slab: Avoid race on slab->obj_exts in alloc_slab_obj_exts
If two competing threads enter alloc_slab_obj_exts() and one of them fails to allocate the object extension vector, it might override the valid slab->obj_exts allocated by the other thread with OBJEXTS_ALLOC_FAIL. This will cause the thread that lost this race and expects a valid pointer to dereference a NULL pointer later on.
Update slab->obj_exts atomically using cmpxchg() to avoid slab->obj_exts overrides by racing threads.
Thanks for Vlastimil and Suren's help with debugging.
Which versions are affected by CVE-2025-40348?
How do I fix CVE-2025-40348?
Apply the vendor's patch.
Is CVE-2025-40348 being exploited?
There is no known exploitation of CVE-2025-40348 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40348, GHSA-468j-fmh4-69r9, UBUNTU-CVE-2025-40348.