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

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

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** Yes
- **Published:** 18 Mar 2026
- **Updated:** 23 May 2026
- **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

## 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: Linux kernel.

## How do I fix CVE-2026-23254?

Apply the vendor's patch.

## Is CVE-2026-23254 being exploited?

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

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23254 and fix it if it is affected.

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

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-23254/ (Markdown: https://insights.sbomify.com/CVE-2026-23254/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23254
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23254
- OSV: https://osv.dev/vulnerability/CVE-2026-23254

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23254/
Summaries are generated and may contain mistakes; the official description above is the record.