# CVE-2026-72256: netfilter: xt_cluster: reject template conntracks in hash match

Status: published. Published: 2026-08-15. Updated: 2026-11-06.

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

netfilter: xt_cluster: reject template conntracks in hash match

xt_cluster_mt() treats any non-NULL nf_ct_get() result as a fully
initialized conntrack and passes it to xt_cluster_hash().

This causes a state confusion bug when the raw table CT target attaches
a template conntrack to skb->_nfct before normal conntrack processing.
Templates carry IPS_TEMPLATE status but do not have a valid tuple for
hashing yet, so xt_cluster_hash() can hit its WARN_ON() path on the
zeroed l3num field.

Reject template conntracks before hashing them. This matches existing
netfilter handling for template objects and avoids hashing incomplete
conntrack state.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 0269ea4937343536ec7e85649932bc8c9686ea78; < 4558bd7b47c7be82dffd837f27be8ea3ecee557d (affected, git); ≥ 0269ea4937343536ec7e85649932bc8c9686ea78; < d5f9d050b0b267227c1f02f11021872c7768a9cc (affected, git); ≥ 0269ea4937343536ec7e85649932bc8c9686ea78; < 4cb8b5f586e41c187942291cc0938006077fa79e (affected, git); ≥ 0269ea4937343536ec7e85649932bc8c9686ea78; < fac2fdac3baad9ffd12b3b0bba4374d4b3585d54 (affected, git); ≥ 0269ea4937343536ec7e85649932bc8c9686ea78; < 13ea4f86cf738c74be2146886ac261988a631e62 (affected, git); ≥ 0269ea4937343536ec7e85649932bc8c9686ea78; < 07f9ddbf5e799c24a3a52ec9bd7b729a6f6d69d5 (affected, git); ≥ 0269ea4937343536ec7e85649932bc8c9686ea78; < 5b2d4f0010018a7aa3495aa1dbf1b7a34011e7aa (affected, git); ≥ 0269ea4937343536ec7e85649932bc8c9686ea78; < 5feba91006ec92da57acc1cc2e34df623b98541e (affected, git). Source: CNA: Linux
- Linux / Linux: 2.6.30 (affected); ≥ 0; < 2.6.30 (unaffected, semver); ≥ 5.10.261; ≤ 5.10.* (unaffected, semver); ≥ 5.15.212; ≤ 5.15.* (unaffected, semver); ≥ 6.1.178; ≤ 6.1.* (unaffected, semver); ≥ 6.6.145; ≤ 6.6.* (unaffected, semver); ≥ 6.12.97; ≤ 6.12.* (unaffected, semver); ≥ 6.18.40; ≤ 6.18.* (unaffected, semver); ≥ 7.1.5; ≤ 7.1.* (unaffected, semver); ≥ 7.2; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.22% as of 2026-11-06; percentile 12.14%

- 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/4558bd7b47c7be82dffd837f27be8ea3ecee557d (CNA: Linux)

- https://git.kernel.org/stable/c/d5f9d050b0b267227c1f02f11021872c7768a9cc (CNA: Linux)

- https://git.kernel.org/stable/c/4cb8b5f586e41c187942291cc0938006077fa79e (CNA: Linux)

- https://git.kernel.org/stable/c/fac2fdac3baad9ffd12b3b0bba4374d4b3585d54 (CNA: Linux)

- https://git.kernel.org/stable/c/13ea4f86cf738c74be2146886ac261988a631e62 (CNA: Linux)

- https://git.kernel.org/stable/c/07f9ddbf5e799c24a3a52ec9bd7b729a6f6d69d5 (CNA: Linux)

- https://git.kernel.org/stable/c/5b2d4f0010018a7aa3495aa1dbf1b7a34011e7aa (CNA: Linux)

- https://git.kernel.org/stable/c/5feba91006ec92da57acc1cc2e34df623b98541e (CNA: Linux)

- https://git.kernel.org/stable/c/07f9ddbf5e799c24a3a52ec9bd7b729a6f6d69d5 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/13ea4f86cf738c74be2146886ac261988a631e62 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/4558bd7b47c7be82dffd837f27be8ea3ecee557d (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/4cb8b5f586e41c187942291cc0938006077fa79e (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/5b2d4f0010018a7aa3495aa1dbf1b7a34011e7aa (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/5feba91006ec92da57acc1cc2e34df623b98541e (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/d5f9d050b0b267227c1f02f11021872c7768a9cc (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

- https://git.kernel.org/stable/c/fac2fdac3baad9ffd12b3b0bba4374d4b3585d54 (416baaa9-dc9f-4396-8d5f-8c081fb06d67)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-72256; retrieved 2026-11-06; source updated 2026-11-06

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72256; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-72256; retrieved 2026-11-06; source updated Not reported

Revision: 2dde8a3e6317ffadbde0f40d471c22b32082ace546845c011d2e19404d11da4c

Canonical: https://y2.dev/cve/CVE-2026-72256

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