CVE-2026-23254 net: gro: fix outer network offset

Medium 5.5 Published 18 Mar 2026 Updated 23 May 2026

A flaw in Linux kernel UDP GRO processing causes checksum errors and potential packet drops, leading to denial of service.

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-2026-23254?

CVE-2026-23254 is a medium-severity denial of service vulnerability in Linux kernel, published on 18 Mar 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: gro: fix outer network offset

The udp GRO complete stage assumes that all the packets inserted the RX have the `encapsulation` flag zeroed. Such assumption is not true, as a few H/W NICs can set such flag when H/W offloading the checksum for an UDP encapsulated traffic, the tun driver can inject GSO packets with UDP encapsulation and the problematic layout can also be created via a veth based setup.

Due to the above, in the problematic scenarios, udp4_gro_complete() uses the wrong network offset (inner instead of outer) to compute the outer UDP header pseudo checksum, leading to csum validation errors later on in packet processing.

Address the issue always clearing the encapsulation flag at GRO completion time. Such flag will be set again as needed for encapsulated packets by udp_gro_complete().

Which versions are affected by CVE-2026-23254?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-23254?

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-2026-23254 being exploited?

There is no known exploitation of CVE-2026-23254 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as BELL-CVE-2026-23254, DEBIAN-CVE-2026-23254, GHSA-wjrj-hvqv-fw2v, ROOT-OS-UBUNTU-2404-CVE-2026-23254, UBUNTU-CVE-2026-23254.