Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-08-15T00:00:00 kernel: netfilter: xt_cluster: reject template conntracks in hash match 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H CWE-843

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.

A flaw was found in the Linux kernel. The `xt_cluster` module, specifically within the `xt_cluster_mt()` function, incorrectly processes template connection tracking (conntrack) objects. This state confusion occurs when a template conntrack is attached before it is fully initialized, leading to `xt_cluster_hash()` attempting to hash incomplete conntrack state. This can cause the system to trigger a `WARN_ON()` condition, potentially resulting in a denial of service.

Red Hat Enterprise Linux 10 Fix deferred kernel Red Hat Enterprise Linux 6 Out of support scope kernel Red Hat Enterprise Linux 7 Fix deferred kernel Red Hat Enterprise Linux 7 Fix deferred kernel-rt Red Hat Enterprise Linux 8 Fix deferred kernel Red Hat Enterprise Linux 8 Fix deferred kernel-rt Red Hat Enterprise Linux 9 Fix deferred kernel Red Hat Enterprise Linux 9 Fix deferred kernel-rt https://www.cve.org/CVERecord?id=CVE-2026-72256 https://nvd.nist.gov/vuln/detail/CVE-2026-72256 https://lore.kernel.org/linux-cve-announce/2026081554-CVE-2026-72256-134f@gregkh/T