# 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.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 4 Dec 2025
- **Updated:** 5 Aug 2026
- **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, ROOT-OS-DEBIAN-13-CVE-2025-40215, ROOT-OS-UBUNTU-2404-CVE-2025-40215, UBUNTU-CVE-2025-40215

## 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.

## Is CVE-2025-40215 being exploited?

There is no known exploitation of CVE-2025-40215 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40215 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2025-40215 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-40215/ (Markdown: https://insights.sbomify.com/CVE-2025-40215/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40215
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40215
- OSV: https://osv.dev/vulnerability/CVE-2025-40215

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40215/
Summaries are generated and may contain mistakes; the official description above is the record.