CVE-2026-98622 net/sched: act_ct: don't WARN on benign flow_offload_alloc() failure
An unprivileged user can crash the system by racing conntrack flushes with traffic control actions if panic_on_warn is enabled.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98622?
CVE-2026-98622 is a denial of service vulnerability in Linux, published on 18 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
net/sched: act_ct: don't WARN on benign flow_offload_alloc() failure
flow_offload_alloc() returns NULL when the conntrack entry is dying (e.g. raced with a conntrack flush) or when the GFP_ATOMIC allocation fails; both are expected under load and neither is a kernel bug. This path runs from softirq on every committed packet, so with panic_on_warn=1 an unprivileged user can panic the box just by racing a conntrack flush against a `tc ... action ct commit` classifier.
Reproduced with a custom repro under QEMU: a small, fixed set of UDP flows through `tc filter ... action ct commit` on lo, raced against threads flooding bare ctnetlink CT_DELETE (flush) requests. Hits WARNING: net/sched/act_ct.c:437 (tcf_ct_flow_table_add(), inlined into tcf_ct_act() in this build) within ~15s on the unpatched kernel; same setup is clean on the patched kernel. The fix itself is behavior-preserving: both branches already did `goto err_alloc` before and after, only the WARN is removed.
Which versions are affected by CVE-2026-98622?
How do I fix CVE-2026-98622?
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-2026-98622 being exploited?
There is no known exploitation of CVE-2026-98622 in the wild and no public exploit code.
Sources
Also known as AZL-108686, BELL-CVE-2026-98622, DEBIAN-CVE-2026-98622, GHSA-qg6m-cv4g-hx6q, UBUNTU-CVE-2026-98622.