medium · CVSS v3 5.5

CVE-2026-98622

This CVE involves a benign warning in the Linux kernel's traffic control conntrack action that can be triggered by an unprivileged user to c

Overview

This CVE involves a benign warning in the Linux kernel's traffic control conntrack action that can be triggered by an unprivileged user to cause a kernel panic when panic_on_warn is enabled. The issue arises when flow_offload_alloc() fails during a conntrack flush race. The patch removes the warning, preventing the panic.

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.

Impact

Confidentiality: none. Integrity: potential denial of service via kernel panic. Availability: system crash. Impacted parties: Linux users running tc with conntrack actions, especially those with panic_on_warn enabled.

Remediation

Apply the kernel patch that removes the WARN; update to a kernel version that includes the fix. If patching is not possible, disable panic_on_warn (set /proc/sys/kernel/panic_on_warn to 0) or avoid using tc action ct commit with conntrack flushes. Monitor for WARN messages in dmesg.

Risk context

Medium severity; no EPSS data; patch available; moderate risk if panic_on_warn enabled.

Affected products

  • Linux kernel

Scores

Severity
medium
CVSS v2
4.9
CVSS v3
5.5
CVSS v4
—
EPSS
—

kernel conntrack tc panic_on_warn denial_of_service Linux traffic_control

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