# CVE-2025-21672: afs: Fix merge preference rule failure condition

> A local attacker can trigger a denial of service in the Linux kernel AFS module by causing a lock to remain held when returning to userspace.

- **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:** 11 May 2026
- **Also known as:** AZL-56285, AZL-56327, BELL-CVE-2025-21672, DEBIAN-CVE-2025-21672, GHSA-94vp-7849-58r6, ROOT-OS-UBUNTU-2204-CVE-2025-21672, UBUNTU-CVE-2025-21672

## What is CVE-2025-21672?

CVE-2025-21672 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:

afs: Fix merge preference rule failure condition

syzbot reported a lock held when returning to userspace[1].  This is
because if argc is less than 0 and the function returns directly, the held
inode lock is not released.

Fix this by store the error in ret and jump to done to clean up instead of
returning directly.

[dh: Modified Lizhi Xu's original patch to make it honour the error code
from afs_split_string()]

[1]
WARNING: lock held when returning to user space!
6.13.0-rc3-syzkaller-00209-g499551201b5f #0 Not tainted
------------------------------------------------
syz-executor133/5823 is leaving the kernel with locks still held!
1 lock held by syz-executor133/5823:
 #0: ffff888071cffc00 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: inode_lock include/linux/fs.h:818 [inline]
 #0: ffff888071cffc00 (&sb->s_type->i_mutex_key#9){++++}-{4:4}, at: afs_proc_addr_prefs_write+0x2bb/0x14e0 fs/afs/addr_prefs.c:388

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2025-21672?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21672?

Apply the vendor's patch.

## Is CVE-2025-21672 being exploited?

There is no known exploitation of CVE-2025-21672 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-2025-21672 and fix it if it is affected.

What it is: CVE-2025-21672 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-2025-21672 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-2025-21672/ (Markdown: https://insights.sbomify.com/CVE-2025-21672/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21672
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21672
- OSV: https://osv.dev/vulnerability/CVE-2025-21672

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21672/
Summaries are generated and may contain mistakes; the official description above is the record.