CVE-2026-72057 net/sched: act_ct: preserve tc_skb_cb across defragmentation
Attackers can cause a kernel panic in Linux systems with panic_on_warn enabled by sending fragmented traffic through the act_ct module.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72057?
CVE-2026-72057 is a high-severity denial of service 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:
net/sched: act_ct: preserve tc_skb_cb across defragmentation
tcf_ct_handle_fragments() calls nf_ct_handle_fragments() without saving and restoring skb->cb. The defrag helper clears IPCB/IP6CB, which aliases the tc_skb_cb/qdisc_skb_cb control buffer. Fragmented traffic through act_ct therefore loses qdisc metadata such as pkt_segs and can trigger WARN_ON_ONCE() in qdisc_pkt_segs() when panic_on_warn is enabled.
Save and restore the full tc_skb_cb around nf_ct_handle_fragments(), matching the pattern used by ovs_ct_handle_fragments().
Weakness: CWE-662
Which versions are affected by CVE-2026-72057?
How do I fix CVE-2026-72057?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-72057 being exploited?
There is no known exploitation of CVE-2026-72057 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72057, DEBIAN-CVE-2026-72057, GHSA-r6mf-v83v-v392, UBUNTU-CVE-2026-72057.