# CVE-2026-31495: netfilter: ctnetlink: use netlink policy range checks

Status: published. Published: 2026-04-22. Updated: 2026-11-05.

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

netfilter: ctnetlink: use netlink policy range checks

Replace manual range and mask validations with netlink policy
annotations in ctnetlink code paths, so that the netlink core rejects
invalid values early and can generate extack errors.

- CTA_PROTOINFO_TCP_STATE: reject values > TCP_CONNTRACK_SYN_SENT2 at
  policy level, removing the manual >= TCP_CONNTRACK_MAX check.
- CTA_PROTOINFO_TCP_WSCALE_ORIGINAL/REPLY: reject values > TCP_MAX_WSCALE
  (14). The normal TCP option parsing path already clamps to this value,
  but the ctnetlink path accepted 0-255, causing undefined behavior when
  used as a u32 shift count.
- CTA_FILTER_ORIG_FLAGS/REPLY_FLAGS: use NLA_POLICY_MASK with
  CTA_FILTER_F_ALL, removing the manual mask checks.
- CTA_EXPECT_FLAGS: use NLA_POLICY_MASK with NF_CT_EXPECT_MASK, adding
  a new mask define grouping all valid expect flags.

Extracted from a broader nf-next patch by Florian Westphal, scoped to
ctnetlink for the fixes tree.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ c8e2078cfe414a99cf6f2f2f1d78c7e75392e9d4; < 435b576cd2faa75154777868f8cbb73bf71644d3 (affected, git); ≥ c8e2078cfe414a99cf6f2f2f1d78c7e75392e9d4; < 2ef71307c86a9f866d6e28f1a0c06e2e9d794474 (affected, git); ≥ c8e2078cfe414a99cf6f2f2f1d78c7e75392e9d4; < 4f7d25f3f0786402ba48ff7d13b6241d77d975f5 (affected, git); ≥ c8e2078cfe414a99cf6f2f2f1d78c7e75392e9d4; < fcec5ce2d73a41668b24e3f18c803541602a59f6 (affected, git); ≥ c8e2078cfe414a99cf6f2f2f1d78c7e75392e9d4; < 675c913b940488a84effdeeac5a1cfb657b59804 (affected, git); ≥ c8e2078cfe414a99cf6f2f2f1d78c7e75392e9d4; < c6cb41eaae875501eaaa487b8db6539feb092292 (affected, git); ≥ c8e2078cfe414a99cf6f2f2f1d78c7e75392e9d4; < 45c33e79ae705b7af97e3117672b6cd258dd0b1b (affected, git); ≥ c8e2078cfe414a99cf6f2f2f1d78c7e75392e9d4; < 8f15b5071b4548b0aafc03b366eb45c9c6566704 (affected, git). Source: CNA: Linux
- Linux / Linux: 2.6.22 (affected); ≥ 0; < 2.6.22 (unaffected, semver); ≥ 5.10.253; ≤ 5.10.* (unaffected, semver); ≥ 5.15.203; ≤ 5.15.* (unaffected, semver); ≥ 6.1.168; ≤ 6.1.* (unaffected, semver); ≥ 6.6.131; ≤ 6.6.* (unaffected, semver); ≥ 6.12.80; ≤ 6.12.* (unaffected, semver); ≥ 6.18.21; ≤ 6.18.* (unaffected, semver); ≥ 6.19.11; ≤ 6.19.* (unaffected, semver); ≥ 7.0; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.5; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP: ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP: ≥ V3.1.5; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP: ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.6; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.5; < * (affected, custom). Source: ADP: siemens-SADP
- Siemens / SIPLUS S7-1500 CPU 1518-4 PN/DP MFP: ≥ V3.1.7; < * (affected, custom). Source: ADP: siemens-SADP

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.13% as of 2026-11-05; percentile 2.53%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/435b576cd2faa75154777868f8cbb73bf71644d3 (CNA: Linux)

- https://git.kernel.org/stable/c/2ef71307c86a9f866d6e28f1a0c06e2e9d794474 (CNA: Linux)

- https://git.kernel.org/stable/c/4f7d25f3f0786402ba48ff7d13b6241d77d975f5 (CNA: Linux)

- https://git.kernel.org/stable/c/fcec5ce2d73a41668b24e3f18c803541602a59f6 (CNA: Linux)

- https://git.kernel.org/stable/c/675c913b940488a84effdeeac5a1cfb657b59804 (CNA: Linux)

- https://git.kernel.org/stable/c/c6cb41eaae875501eaaa487b8db6539feb092292 (CNA: Linux)

- https://git.kernel.org/stable/c/45c33e79ae705b7af97e3117672b6cd258dd0b1b (CNA: Linux)

- https://git.kernel.org/stable/c/8f15b5071b4548b0aafc03b366eb45c9c6566704 (CNA: Linux)

- https://cert-portal.siemens.com/productcert/html/ssa-082556.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-019113.html (ADP: siemens-SADP)

- https://cert-portal.siemens.com/productcert/html/ssa-457936.html (ADP: siemens-SADP)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-31495; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-31495; retrieved 2026-11-05; source updated Not reported

Revision: 97236a4efc8aea59682377a1ce3d10115ab99fe163338455b45167a59292b519

Canonical: https://y2.dev/cve/CVE-2026-31495

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.