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Medium 5.5

Vulnerability in Linux kernel

CVE-2025-21706 First seen on SecPulse

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-2025-21706 has been found in Linux kernel.
Risk of unauthorized operations or information disclosure. CVSS score: 5.5/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Linux kernel CVE-2025-21706" on the vendor's site.

CVE-2025-21706 (Linux kernel) — CVSS v3 5.5
Attack vector: local / no user interaction
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 Linux kernel.

Affected scope

Check the vendor advisory for the affected versions of Linux kernel.

Severity

Severity: Medium (CVSS 5.5/10). Risk of unauthorized operations or information disclosure.

How to fix

Update to the patched release per vendor advisory.

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. Audit SBOM/dependencies to find affected services.

Response actions

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

  1. 1
    Identify exposureidentify
    Audit SBOM/dependencies for affected components.

    資産台帳・SBOM・依存マニフェストで Linux kernel を使っているサービスとバージョンを洗い出す。

  2. 2
    Post-deployment verificationverify
    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

EcosystemPackageAffectedFixed
Linux Kernel
≥ 5.18.0, < 6.1.129
≥ 6.2.0, < 6.6.78
≥ 6.7.0, < 6.12.13
≥ 6.13.0, < 6.13.2
6.1.129
6.6.78
6.12.13
6.13.2

Fix status by distribution

Fixed packages published by each distribution for this CVE

Original description The description as published by the source.

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

mptcp: pm: only set fullmesh for subflow endp

With the in-kernel path-manager, it is possible to change the 'fullmesh'
flag. The code in mptcp_pm_nl_fullmesh() expects to change it only on
'subflow' endpoints, to recreate more or less subflows using the linked
address.

Unfortunately, the set_flags() hook was a bit more permissive, and
allowed 'implicit' endpoints to get the 'fullmesh' flag while it is not
allowed before.

That's what syzbot found, triggering the following warning:

WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 __mark_subflow_endp_available net/mptcp/pm_netlink.c:1496 [inline]
WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 mptcp_pm_nl_fullmesh net/mptcp/pm_netlink.c:1980 [inline]
WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 mptcp_nl_set_flags net/mptcp/pm_netlink.c:2003 [inline]
WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 mptcp_pm_nl_set_flags+0x974/0xdc0 net/mptcp/pm_netlink.c:2064
Modules linked in:
CPU: 0 UID: 0 PID: 6499 Comm: syz.1.413 Not tainted 6.13.0-rc5-syzkaller-00172-gd1bf27c4e176 #0
Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
RIP: 0010:__mark_subflow_endp_available net/mptcp/pm_netlink.c:1496 [inline]
RIP: 0010:mptcp_pm_nl_fullmesh net/mptcp/pm_netlink.c:1980 [inline]
RIP: 0010:mptcp_nl_set_flags net/mptcp/pm_netlink.c:2003 [inline]
RIP: 0010:mptcp_pm_nl_set_flags+0x974/0x…

Source: NIST National Vulnerability Database NVD GitHub Advisory

References

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