Vulnerability in Kernel (CVE-2026-23406)

Summary

Vulnerability in Kernel (CVE-2026-23406). Successful exploitation can lead to full system takeover. Mitigation: upgrade to 5.10.253, 5.15.203, 6.1.169, 6.6.130, 6.12.77, 6.18.18, 6.19.8 or later.

Original description

The description as published by the source.

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

apparmor: fix side-effect bug in match_char() macro usage

The match_char() macro evaluates its character parameter multiple
times when traversing differential encoding chains. When invoked
with *str++, the string pointer advances on each iteration of the
inner do-while loop, causing the DFA to check different characters
at each iteration and therefore skip input characters.
This results in out-of-bounds reads when the pointer advances past
the input buffer boundary.

[ 94.984676] ==================================================================
[ 94.985301] BUG: KASAN: slab-out-of-bounds in aa_dfa_match+0x5ae/0x760
[ 94.985655] Read of size 1 at addr ffff888100342000 by task file/976

[ 94.986319] CPU: 7 UID: 1000 PID: 976 Comm: file Not tainted 6.19.0-rc7-next-20260127 #1 PREEMPT(lazy)
[ 94.986322] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[ 94.986329] Call Trace:
[ 94.986341]
[ 94.986347] dump_stack_lvl+0x5e/0x80
[ 94.986374] print_report+0xc8/0x270
[ 94.986384] ? aa_dfa_match+0x5ae/0x760
[ 94.986388] kasan_report+0x118/0x150
[ 94.986401] ? aa_dfa_match+0x5ae/0x760
[ 94.986405] aa_dfa_match+0x5ae/0x760
[ 94.986408] __aa_path_perm+0x131/0x400
[ 94.986418] aa_path_perm+0x219/0x2f0
[ 94.986424] apparmor_file_open+0x345/0x570
[ 94.986431] security_file_open+0x5c/0x140
[ 94.986442] do_dentry_open+0x2f6/0x1120
[…

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-2026-23406 has been found in Kernel.
Successful exploitation can lead to full system takeover.
What to do: upgrade Kernel to 5.10.253, 5.15.203, 6.1.169, 6.6.130, 6.12.77, 6.18.18, 6.19.8 or later.
If unsure, ask your IT team or search "Kernel CVE-2026-23406" on the vendor's site.

CVE-2026-23406 (Kernel)
Attack vector: local / no user interaction
Patched: 5.10.253, 5.15.203, 6.1.169, 6.6.130, 6.12.77, 6.18.18, 6.19.8 — 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: ?. Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 5.10.253, 5.15.203, 6.1.169, 6.6.130, 6.12.77, 6.18.18, 6.19.8.

🛡️ 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 5.10.253, 5.15.203, 6.1.169, 6.6.130, 6.12.77, 6.18.18, 6.19.8
```
ステージング環境で 5.10.253, 5.15.203, 6.1.169, 6.6.130, 6.12.77, 6.18.18, 6.19.8 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":"4.17.0"},{"fixed":"5.10.253"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.203"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.169"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.130"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.77"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.18"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.8"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

BellSoft Alpaquita BELL-CVE-2026-23406 linux-lts Fixed in: 6.1.170-r0
Debian DEBIAN-CVE-2026-23406 linux Fixed in: 5.10.251-1
Ubuntu UBUNTU-CVE-2026-23406 linux-hwe-edge