# CVE-2026-64541: net/smc: fix UAF in smc_cdc_rx_handler() by pinning the socket

> A use-after-free in the Linux kernel's SMC-R protocol allows attackers to cause a kernel panic or potentially execute code via race conditions.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 27 Jul 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-94026, BELL-CVE-2026-64541, DEBIAN-CVE-2026-64541, GHSA-wjv3-3r54-x298, ROOT-OS-DEBIAN-12-CVE-2026-64541, UBUNTU-CVE-2026-64541

## What is CVE-2026-64541?

CVE-2026-64541 is a critical use after free vulnerability in Linux, published on 27 Jul 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 UAF in smc_cdc_rx_handler() by pinning the socket

smc_cdc_rx_handler() looks up the connection by token under the link
group's conns_lock, drops the lock, and then dereferences conn and the
smc_sock derived from it, ending in sock_hold(&smc->sk) inside
smc_cdc_msg_recv(). No reference is held across the lock release.

The only reference pinning the socket while the connection is
discoverable in the link group is taken in smc_lgr_register_conn()
(sock_hold) and dropped in __smc_lgr_unregister_conn() (sock_put), both
under conns_lock. Once the handler drops conns_lock, a concurrent
close() -> smc_release() -> smc_conn_free() -> smc_lgr_unregister_conn()
can drop that reference and free the smc_sock, so the handler's later
sock_hold() runs on freed memory:

  WARNING: lib/refcount.c:25 at refcount_warn_saturate
  Workqueue: rxe_wq do_work
   refcount_warn_saturate (lib/refcount.c:25)
   smc_cdc_msg_recv (net/smc/smc_cdc.c:430)
   smc_cdc_rx_handler (net/smc/smc_cdc.c:502)
   smc_wr_rx_tasklet_fn (net/smc/smc_wr.c:445)
   tasklet_action_common (kernel/softirq.c:938)
   handle_softirqs (kernel/softirq.c:622)
  Kernel panic - not syncing: panic_on_warn set

Only SMC-R is affected. The SMC-D receive tasklet is stopped by
tasklet_kill(&conn->rx_tsklet) in smc_conn_free() before the connection
is unregistered, so it cannot run concurrently with the free.

Take the socket reference while still holding conns_lock, so the
registration reference can no longer be the last one, and drop it once
the handler is done.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-64541?


## How do I fix CVE-2026-64541?

Apply the vendor's patch.

## Is CVE-2026-64541 being exploited?

There is no known exploitation of CVE-2026-64541 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64541 and fix it if it is affected.

What it is: CVE-2026-64541 is a critical use after free vulnerability in Linux, published on 27 Jul 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-2026-64541 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-2026-64541/ (Markdown: https://insights.sbomify.com/CVE-2026-64541/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64541
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64541
- OSV: https://osv.dev/vulnerability/CVE-2026-64541

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64541/
Summaries are generated and may contain mistakes; the official description above is the record.