Vulnerability in Kernel (CVE-2025-21891)

Summary

Vulnerability in Kernel (CVE-2025-21891). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 6.1.130, 6.6.81, 6.12.18, 6.13.6 or later.

Original description

The description as published by the source.

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

ipvlan: ensure network headers are in skb linear part

syzbot found that ipvlan_process_v6_outbound() was assuming
the IPv6 network header isis present in skb->head [1]

Add the needed pskb_network_may_pull() calls for both
IPv4 and IPv6 handlers.

[1]
BUG: KMSAN: uninit-value in __ipv6_addr_type+0xa2/0x490 net/ipv6/addrconf_core.c:47
__ipv6_addr_type+0xa2/0x490 net/ipv6/addrconf_core.c:47
ipv6_addr_type include/net/ipv6.h:555 [inline]
ip6_route_output_flags_noref net/ipv6/route.c:2616 [inline]
ip6_route_output_flags+0x51/0x720 net/ipv6/route.c:2651
ip6_route_output include/net/ip6_route.h:93 [inline]
ipvlan_route_v6_outbound+0x24e/0x520 drivers/net/ipvlan/ipvlan_core.c:476
ipvlan_process_v6_outbound drivers/net/ipvlan/ipvlan_core.c:491 [inline]
ipvlan_process_outbound drivers/net/ipvlan/ipvlan_core.c:541 [inline]
ipvlan_xmit_mode_l3 drivers/net/ipvlan/ipvlan_core.c:605 [inline]
ipvlan_queue_xmit+0xd72/0x1780 drivers/net/ipvlan/ipvlan_core.c:671
ipvlan_start_xmit+0x5b/0x210 drivers/net/ipvlan/ipvlan_main.c:223
__netdev_start_xmit include/linux/netdevice.h:5150 [inline]
netdev_start_xmit include/linux/netdevice.h:5159 [inline]
xmit_one net/core/dev.c:3735 [inline]
dev_hard_start_xmit+0x247/0xa20 net/core/dev.c:3751
sch_direct_xmit+0x399/0xd40 net/sched/sch_generic.c:343
qdisc_restart net/sched/sch_generic.c:408 [inline]
__qdisc_run+0x14da/0x35d0 net/sched/sch_generic.c:416…

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-2025-21891 has been found in Kernel.
Risk of unauthorized operations or information disclosure.
What to do: upgrade Kernel to 6.1.130, 6.6.81, 6.12.18, 6.13.6 or later.
If unsure, ask your IT team or search "Kernel CVE-2025-21891" on the vendor's site.

CVE-2025-21891 (Kernel)
Attack vector: local / no user interaction
Patched: 6.1.130, 6.6.81, 6.12.18, 6.13.6 — 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 6.1.130, 6.6.81, 6.12.18, 6.13.6.

🛡️ 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 6.1.130, 6.6.81, 6.12.18, 6.13.6
```
ステージング環境で 6.1.130, 6.6.81, 6.12.18, 6.13.6 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":"3.19.0"},{"fixed":"6.1.130"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.81"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.18"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.13.6"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

BellSoft Alpaquita BELL-CVE-2025-21891 linux-lts Fixed in: 6.1.130-r0
Debian DEBIAN-CVE-2025-21891 linux
Ubuntu UBUNTU-CVE-2025-21891 linux-aws