# CVE-2026-74692: net/smc: fix TOCTOU race between smc_listen_out() and listener close

> A race condition in the Linux kernel SMC module allows remote attackers to exhaust kernel memory and cause denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-97083, BELL-CVE-2026-74692, DEBIAN-CVE-2026-74692, GHSA-r9r5-95ff-67hq, UBUNTU-CVE-2026-74692

## What is CVE-2026-74692?

CVE-2026-74692 is a high-severity vulnerability in Linux, published on 22 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

net/smc: fix TOCTOU race between smc_listen_out() and listener close

smc_listen_out() reads lsmc->sk.sk_state without the listener lock,
then acquires lock_sock_nested() only after the check passes. This
opens a window where smc_close_active() can transition the listener
to SMC_CLOSED, call smc_close_cleanup_listen() to drain the accept
queue, and release the lock, all between the lockless read and the
delayed lock acquisition:

  smc_listen_work (smc_hs_wq)          smc_close_active()
  -------------------------------      -------------------------
  release_sock(child)
  if (sk_state == SMC_LISTEN) TRUE
                                        lock_sock(listener)
                                        sk_state = SMC_CLOSED
                                        smc_close_cleanup_listen()
                                        release_sock(listener)
                                        flush_work(tcp_listen_work)
  lock_sock_nested(listener)
  smc_accept_enqueue(listener, child) /* child enqueued on dead listener */

smc_close_active() flushes only tcp_listen_work. Work items already
dispatched onto smc_hs_wq for the CLC handshake continue running
unguarded. smc_accept_enqueue() takes a sock_hold() on the child that
is never released, so the child smc_sock, its clcsock, and the
reference all leak. A remote peer that opens TCP connections while the
server calls close() can exhaust kernel memory.

Move lock_sock_nested() to before the sk_state check so that the test
and the enqueue are atomic under the listener lock.

## Which versions are affected by CVE-2026-74692?


## How do I fix CVE-2026-74692?

Apply the vendor's patch.

## Is CVE-2026-74692 being exploited?

There is no known exploitation of CVE-2026-74692 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74692 and fix it if it is affected.

What it is: CVE-2026-74692 is a high-severity vulnerability in Linux, published on 22 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74692 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-2026-74692/ (Markdown: https://insights.sbomify.com/CVE-2026-74692/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74692
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74692
- OSV: https://osv.dev/vulnerability/CVE-2026-74692

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74692/
Summaries are generated and may contain mistakes; the official description above is the record.