CVE-2026-72256 netfilter: xt_cluster: reject template conntracks in hash match
A flaw in the Linux kernel netfilter module allows remote attackers to cause a denial of service by triggering a null dereference in the cluster match hash function.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72256?
CVE-2026-72256 is a vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-72256?
How do I fix CVE-2026-72256?
Apply the vendor's patch.
Is CVE-2026-72256 being exploited?
There is no known exploitation of CVE-2026-72256 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72256, DEBIAN-CVE-2026-72256, GHSA-hh4g-5q85-w496, UBUNTU-CVE-2026-72256.