Use-After-Free in Linux kernel (CVE-2026-31504)
Summary
Vulnerability in Linux kernel (CVE-2026-31504). Successful exploitation can lead to full system takeover. Exploitable via NETDEV_UP.
Original description
The description as published by the source.
In the Linux kernel, the following vulnerability has been resolved:
net: fix fanout UAF in packet_release() via NETDEV_UP race
packet_release() has a race window where NETDEV_UP can re-register a
socket into a fanout group's arr[] array. The re-registration is not
cleaned up by fanout_release(), leaving a dangling pointer in the fanout
array.
packet_release() does NOT zero po->num in its bind_lock section.
After releasing bind_lock, po->num is still non-zero and po->ifindex
still matches the bound device. A concurrent packet_notifier(NETDEV_UP)
that already found the socket in sklist can re-register the hook.
For fanout sockets, this re-registration calls __fanout_link(sk, po)
which adds the socket back into f->arr[] and increments f->num_members,
but does NOT increment f->sk_ref.
The fix sets po->num to zero in packet_release while bind_lock is
held to prevent NETDEV_UP from linking, preventing the race window.
This bug was found following an additional audit with Claude Code based
on CVE-2025-38617.
Source: NIST National Vulnerability Database NVD GitHub Advisory
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-2026-31504 has been found in Linux kernel.
Attackers can target a specific entry point like NETDEV_UP over the network to misuse the product.
Successful exploitation can lead to full system takeover. CVSS score: 7.8/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Linux kernel CVE-2026-31504" on the vendor's site.
CVE-2026-31504 (Linux kernel) — CWE-416 / CVSS v3 7.8
Attack vector: local / no user interaction
Attack surface: NETDEV_UP / bind_lock / sklist / packet_release
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.
Use-after-free (CWE-416) exists in Linux kernel. Attackers reach the vulnerable code path via NETDEV_UP.
Check the vendor advisory for the affected versions of Linux kernel. Attack surface: NETDEV_UP / bind_lock / sklist / packet_release.
Severity: High (CVSS 7.8/10). Successful exploitation can lead to full system takeover.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
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
-
1Identify exposure identify
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。
-
2Post-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
Fix status by distribution
Fixed packages published by each distribution for this CVE
- BellSoft Alpaquita BELL-CVE-2026-31504 linux-lts Fixed in: 6.1.168-r0
- Debian DEBIAN-CVE-2026-31504 linux Fixed in: 5.10.257-1
- Ubuntu UBUNTU-CVE-2026-31504 linux
References
- advisory nvd.nist.gov
- advisory github.com
- package git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web git.kernel.org
- web cert-portal.siemens.com
- web cert-portal.siemens.com
- web github.com
- web cert-portal.siemens.com