CVE-2025-40215 xfrm: delete x->tunnel as we delete x
A use-after-free vulnerability in the Linux kernel's xfrm subsystem can cause a kernel warning and potential denial of service during network namespace cleanup.
- 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-2025-40215?
CVE-2025-40215 is a high-severity use after free vulnerability in Linux, published on 4 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:
xfrm: delete x->tunnel as we delete x
The ipcomp fallback tunnels currently get deleted (from the various lists and hashtables) as the last user state that needed that fallback is destroyed (not deleted). If a reference to that user state still exists, the fallback state will remain on the hashtables/lists, triggering the WARN in xfrm_state_fini. Because of those remaining references, the fix in commit f75a2804da39 ("xfrm: destroy xfrm_state synchronously on net exit path") is not complete.
We recently fixed one such situation in TCP due to defered freeing of skbs (commit 9b6412e6979f ("tcp: drop secpath at the same time as we currently drop dst")). This can also happen due to IP reassembly: skbs with a secpath remain on the reassembly queue until netns destruction. If we can't guarantee that the queues are flushed by the time xfrm_state_fini runs, there may still be references to a (user) xfrm_state, preventing the timely deletion of the corresponding fallback state.
Instead of chasing each instance of skbs holding a secpath one by one, this patch fixes the issue directly within xfrm, by deleting the fallback state as soon as the last user state depending on it has been deleted. Destruction will still happen when the final reference is dropped.
A separate lockdep class for the fallback state is required since we're going to lock x->tunnel while x is locked.
Which versions are affected by CVE-2025-40215?
How do I fix CVE-2025-40215?
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-2025-40215 being exploited?
There is no known exploitation of CVE-2025-40215 in the wild and no public exploit code.
Sources
Also known as AZL-71281, BELL-CVE-2025-40215, DEBIAN-CVE-2025-40215, GHSA-346r-c6v5-7g38, ROOT-OS-DEBIAN-11-CVE-2025-40215, ROOT-OS-DEBIAN-12-CVE-2025-40215 and 3 more.