# CVE-2025-21751: net/mlx5: HWS, change error flow on matcher disconnect

> A use-after-free vulnerability in the Linux kernel mlx5 driver allows a local attacker to cause a system crash via firmware failure during matcher disconnect.

- **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:** 27 Feb 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-21751, DEBIAN-CVE-2025-21751, GHSA-6cpx-w2cg-qmgr, ROOT-OS-DEBIAN-11-CVE-2025-21751, ROOT-OS-DEBIAN-12-CVE-2025-21751, ROOT-OS-DEBIAN-13-CVE-2025-21751, ROOT-OS-UBUNTU-2204-CVE-2025-21751, ROOT-OS-UBUNTU-2404-CVE-2025-21751, UBUNTU-CVE-2025-21751

## What is CVE-2025-21751?

CVE-2025-21751 is a high-severity use after free vulnerability in Linux kernel, published on 27 Feb 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:

net/mlx5: HWS, change error flow on matcher disconnect

Currently, when firmware failure occurs during matcher disconnect flow,
the error flow of the function reconnects the matcher back and returns
an error, which continues running the calling function and eventually
frees the matcher that is being disconnected.
This leads to a case where we have a freed matcher on the matchers list,
which in turn leads to use-after-free and eventual crash.

This patch fixes that by not trying to reconnect the matcher back when
some FW command fails during disconnect.

Note that we're dealing here with FW error. We can't overcome this
problem. This might lead to bad steering state (e.g. wrong connection
between matchers), and will also lead to resource leakage, as it is
the case with any other error handling during resource destruction.

However, the goal here is to allow the driver to continue and not crash
the machine with use-after-free error.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2025-21751?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21751?

Apply the vendor's patch.

## Is CVE-2025-21751 being exploited?

There is no known exploitation of CVE-2025-21751 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-2025-21751 and fix it if it is affected.

What it is: CVE-2025-21751 is a high-severity use after free vulnerability in Linux kernel, published on 27 Feb 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-2025-21751 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-2025-21751/ (Markdown: https://insights.sbomify.com/CVE-2025-21751/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21751
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21751
- OSV: https://osv.dev/vulnerability/CVE-2025-21751

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21751/
Summaries are generated and may contain mistakes; the official description above is the record.