# CVE-2025-21646: afs: Fix the maximum cell name length

> A flaw in the Linux kernel AFS filesystem allows a local attacker to trigger a kernel warning and potential denial of service by using a cell name exceeding the procfs filename limit.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jan 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-21646, DEBIAN-CVE-2025-21646, GHSA-qwq3-wccv-85hw, UBUNTU-CVE-2025-21646

## What is CVE-2025-21646?

CVE-2025-21646 is a high-severity denial of service vulnerability in Linux kernel, published on 19 Jan 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

afs: Fix the maximum cell name length

The kafs filesystem limits the maximum length of a cell to 256 bytes, but a
problem occurs if someone actually does that: kafs tries to create a
directory under /proc/net/afs/ with the name of the cell, but that fails
with a warning:

        WARNING: CPU: 0 PID: 9 at fs/proc/generic.c:405

because procfs limits the maximum filename length to 255.

However, the DNS limits the maximum lookup length and, by extension, the
maximum cell name, to 255 less two (length count and trailing NUL).

Fix this by limiting the maximum acceptable cellname length to 253.  This
also allows us to be sure we can create the "/afs/.<cell>/" mountpoint too.

Further, split the YFS VL record cell name maximum to be the 256 allowed by
the protocol and ignore the record retrieved by YFSVL.GetCellName if it
exceeds 253.

## Which versions are affected by CVE-2025-21646?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21646?

Apply the vendor's patch.

## Is CVE-2025-21646 being exploited?

There is no known exploitation of CVE-2025-21646 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-2025-21646 and fix it if it is affected.

What it is: CVE-2025-21646 is a high-severity denial of service vulnerability in Linux kernel, published on 19 Jan 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-21646 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-2025-21646/ (Markdown: https://insights.sbomify.com/CVE-2025-21646/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21646
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21646
- OSV: https://osv.dev/vulnerability/CVE-2025-21646

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21646/
Summaries are generated and may contain mistakes; the official description above is the record.