CVE-2026-31684 net: sched: act_csum: validate nested VLAN headers

Medium 5.5 Published 25 Apr 2026 Updated 1 Jun 2026

A missing bounds check in the Linux kernel's traffic control checksum action allows out-of-bounds reads and potential memory corruption when processing nested VLAN headers.

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-2026-31684?

CVE-2026-31684 is a medium-severity memory corruption vulnerability in Linux kernel, published on 25 Apr 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_csum: validate nested VLAN headers

tcf_csum_act() walks nested VLAN headers directly from skb->data when an skb still carries in-payload VLAN tags. The current code reads vlan->h_vlan_encapsulated_proto and then pulls VLAN_HLEN bytes without first ensuring that the full VLAN header is present in the linear area.

If only part of an inner VLAN header is linearized, accessing h_vlan_encapsulated_proto reads past the linear area, and the following skb_pull(VLAN_HLEN) may violate skb invariants.

Fix this by requiring pskb_may_pull(skb, VLAN_HLEN) before accessing and pulling each nested VLAN header. If the header still is not fully available, drop the packet through the existing error path.

Which versions are affected by CVE-2026-31684?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-31684?

Apply the vendor's patch.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2026-31684 being exploited?

There is no known exploitation of CVE-2026-31684 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as AZL-84222, BELL-CVE-2026-31684, DEBIAN-CVE-2026-31684, GHSA-gj33-f2q3-mjhg, ROOT-OS-DEBIAN-11-CVE-2026-31684, ROOT-OS-DEBIAN-12-CVE-2026-31684 and 3 more.