# CVE-2026-74262: kcm: use WRITE_ONCE() when changing lower socket callbacks

> A race condition in the Linux kernel's KCM module can cause stale or misdirected wakeups due to unsynchronized socket callback updates.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-74262, DEBIAN-CVE-2026-74262, GHSA-rv7w-h679-g92g, UBUNTU-CVE-2026-74262

## What is CVE-2026-74262?

CVE-2026-74262 is a high-severity vulnerability in Linux, published on 15 Aug 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:

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.

## Which versions are affected by CVE-2026-74262?


## How do I fix CVE-2026-74262?

Apply the vendor's patch.

## Is CVE-2026-74262 being exploited?

There is no known exploitation of CVE-2026-74262 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74262 and fix it if it is affected.

What it is: CVE-2026-74262 is a high-severity vulnerability in Linux, published on 15 Aug 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-2026-74262 in the wild and no public exploit code.

Affected product: Linux. 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-2026-74262/ (Markdown: https://insights.sbomify.com/CVE-2026-74262/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74262
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74262
- OSV: https://osv.dev/vulnerability/CVE-2026-74262

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74262/
Summaries are generated and may contain mistakes; the official description above is the record.