Vulnerability in Kernel (CVE-2025-21721)

Summary

Vulnerability in Kernel (CVE-2025-21721). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 5.4.291, 5.10.235, 5.15.179, 6.1.131, 6.6.80, 6.12.13, 6.13.2 or later.

Original description

The description as published by the source.

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

nilfs2: handle errors that nilfs_prepare_chunk() may return

Patch series "nilfs2: fix issues with rename operations".

This series fixes BUG_ON check failures reported by syzbot around rename
operations, and a minor behavioral issue where the mtime of a child
directory changes when it is renamed instead of moved.

This patch (of 2):

The directory manipulation routines nilfs_set_link() and
nilfs_delete_entry() rewrite the directory entry in the folio/page
previously read by nilfs_find_entry(), so error handling is omitted on the
assumption that nilfs_prepare_chunk(), which prepares the buffer for
rewriting, will always succeed for these. And if an error is returned, it
triggers the legacy BUG_ON() checks in each routine.

This assumption is wrong, as proven by syzbot: the buffer layer called by
nilfs_prepare_chunk() may call nilfs_get_block() if necessary, which may
fail due to metadata corruption or other reasons. This has been there all
along, but improved sanity checks and error handling may have made it more
reproducible in fuzzing tests.

Fix this issue by adding missing error paths in nilfs_set_link(),
nilfs_delete_entry(), and their caller nilfs_rename().

Source: OSV.dev (Open Source Vulnerabilities) NVD OSV

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2025-21721 has been found in Kernel.
Risk of unauthorized operations or information disclosure.
What to do: upgrade Kernel to 5.4.291, 5.10.235, 5.15.179, 6.1.131, 6.6.80, 6.12.13, 6.13.2 or later.
If unsure, ask your IT team or search "Kernel CVE-2025-21721" on the vendor's site.

CVE-2025-21721 (Kernel)
Patched: 5.4.291, 5.10.235, 5.15.179, 6.1.131, 6.6.80, 6.12.13, 6.13.2 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (unclassified) exists in Kernel.

📍 Affected scope

Check the vendor advisory for the affected versions of Kernel.

🔥 Severity

Severity: ?. Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 5.4.291, 5.10.235, 5.15.179, 6.1.131, 6.6.80, 6.12.13, 6.13.2.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'Kernel' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

1
Identify exposure identify
```
grep -r 'Kernel' . | grep -v node_modules
```
リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で Kernel を grep し、稼働しているサービス・バージョンを把握する。
2
Apply patch patch
```
Upgrade Kernel to 5.4.291, 5.10.235, 5.15.179, 6.1.131, 6.6.80, 6.12.13, 6.13.2
```
ステージング環境で 5.4.291, 5.10.235, 5.15.179, 6.1.131, 6.6.80, 6.12.13, 6.13.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
3
Post-deployment verification verify
```
Confirm patched version is live in production
```
パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

Linux Kernel

[{"type":"ECOSYSTEM","events":[{"introduced":"2.6.30"},{"fixed":"5.4.291"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.5.0"},{"fixed":"5.10.235"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.179"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.131"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.80"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.13"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.13.2"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

BellSoft Alpaquita BELL-CVE-2025-21721 linux-lts Fixed in: 6.1.131-r0
Debian DEBIAN-CVE-2025-21721 linux Fixed in: 5.10.237-1
Ubuntu UBUNTU-CVE-2025-21721 linux