# CVE-2025-21666: vsock: prevent null-ptr-deref in vsock_*[has_data|has_space]

> A null pointer dereference in the Linux kernel vsock subsystem can cause a system crash, requiring a kernel patch to prevent denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 31 Jan 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-56279, AZL-56337, BELL-CVE-2025-21666, DEBIAN-CVE-2025-21666, GHSA-p6f8-9m89-hwvw, UBUNTU-CVE-2025-21666

## What is CVE-2025-21666?

CVE-2025-21666 is a medium-severity vulnerability in Linux kernel, published on 31 Jan 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: prevent null-ptr-deref in vsock_*[has_data|has_space]

Recent reports have shown how we sometimes call vsock_*_has_data()
when a vsock socket has been de-assigned from a transport (see attached
links), but we shouldn't.

Previous commits should have solved the real problems, but we may have
more in the future, so to avoid null-ptr-deref, we can return 0
(no space, no data available) but with a warning.

This way the code should continue to run in a nearly consistent state
and have a warning that allows us to debug future problems.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2025-21666?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21666?

Apply the vendor's patch.

## Is CVE-2025-21666 being exploited?

There is no known exploitation of CVE-2025-21666 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-21666 and fix it if it is affected.

What it is: CVE-2025-21666 is a medium-severity vulnerability in Linux kernel, published on 31 Jan 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-2025-21666 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2025-21666/ (Markdown: https://insights.sbomify.com/CVE-2025-21666/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21666
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21666
- OSV: https://osv.dev/vulnerability/CVE-2025-21666

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21666/
Summaries are generated and may contain mistakes; the official description above is the record.