Vulnerability in Kernel (CVE-2025-21840)

Summary

Vulnerability in Kernel (CVE-2025-21840). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 6.13.4 or later.

Original description

The description as published by the source.

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

thermal/netlink: Prevent userspace segmentation fault by adjusting UAPI header

The intel-lpmd tool [1], which uses the THERMAL_GENL_ATTR_CPU_CAPABILITY
attribute to receive HFI events from kernel space, encounters a
segmentation fault after commit 1773572863c4 ("thermal: netlink: Add the
commands and the events for the thresholds").

The issue arises because the THERMAL_GENL_ATTR_CPU_CAPABILITY raw value
was changed while intel_lpmd still uses the old value.

Although intel_lpmd can be updated to check the THERMAL_GENL_VERSION and
use the appropriate THERMAL_GENL_ATTR_CPU_CAPABILITY value, the commit
itself is questionable.

The commit introduced a new element in the middle of enum thermal_genl_attr,
which affects many existing attributes and introduces potential risks
and unnecessary maintenance burdens for userspace thermal netlink event
users.

Solve the issue by moving the newly introduced
THERMAL_GENL_ATTR_TZ_PREV_TEMP attribute to the end of the
enum thermal_genl_attr. This ensures that all existing thermal generic
netlink attributes remain unaffected.

[ rjw: Subject edits ]

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-2025-21840 has been found in Kernel.
Risk of unauthorized operations or information disclosure.
What to do: upgrade Kernel to 6.13.4 or later.
If unsure, ask your IT team or search "Kernel CVE-2025-21840" on the vendor's site.

CVE-2025-21840 (Kernel)
Patched: 6.13.4 — 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 6.13.4.

🛡️ 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 6.13.4
```
ステージング環境で 6.13.4 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":"6.13.0"},{"fixed":"6.13.4"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

BellSoft Alpaquita BELL-CVE-2025-21840 linux-lts Fixed in: 6.18.35-r1