# CVE-2025-40231: vsock: fix lock inversion in vsock_assign_transport()

> A local attacker can trigger a deadlock in the Linux kernel vsock subsystem, causing a denial of service.

- **Severity:** Not scored
- **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:** 23 May 2026
- **Also known as:** BELL-CVE-2025-40231, DEBIAN-CVE-2025-40231, GHSA-mpc4-rxjp-4rpf, ROOT-OS-DEBIAN-11-CVE-2025-40231, ROOT-OS-UBUNTU-2404-CVE-2025-40231, UBUNTU-CVE-2025-40231

## What is CVE-2025-40231?

CVE-2025-40231 is a 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:

vsock: fix lock inversion in vsock_assign_transport()

Syzbot reported a potential lock inversion deadlock between
vsock_register_mutex and sk_lock-AF_VSOCK when vsock_linger() is called.

The issue was introduced by commit 687aa0c5581b ("vsock: Fix
transport_* TOCTOU") which added vsock_register_mutex locking in
vsock_assign_transport() around the transport->release() call, that can
call vsock_linger(). vsock_assign_transport() can be called with sk_lock
held. vsock_linger() calls sk_wait_event() that temporarily releases and
re-acquires sk_lock. During this window, if another thread hold
vsock_register_mutex while trying to acquire sk_lock, a circular
dependency is created.

Fix this by releasing vsock_register_mutex before calling
transport->release() and vsock_deassign_transport(). This is safe
because we don't need to hold vsock_register_mutex while releasing the
old transport, and we ensure the new transport won't disappear by
obtaining a module reference first via try_module_get().

## Which versions are affected by CVE-2025-40231?


## How do I fix CVE-2025-40231?

Apply the vendor's patch.

## Is CVE-2025-40231 being exploited?

There is no known exploitation of CVE-2025-40231 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40231 and fix it if it is affected.

What it is: CVE-2025-40231 is a 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-2025-40231 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-2025-40231/ (Markdown: https://insights.sbomify.com/CVE-2025-40231/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40231
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40231
- OSV: https://osv.dev/vulnerability/CVE-2025-40231

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40231/
Summaries are generated and may contain mistakes; the official description above is the record.