# CVE-2025-40139: smc: Use __sk_dst_get() and dst_dev_rcu() in in smc_clc_prfx_set().

> A use-after-free vulnerability in the Linux kernel's SMC protocol allows attackers to potentially execute code or cause a denial of service during connection setup.

- **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:** 12 Nov 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-69998, BELL-CVE-2025-40139, DEBIAN-CVE-2025-40139, GHSA-ffj5-vpjf-2hxm, ROOT-OS-DEBIAN-11-CVE-2025-40139, ROOT-OS-DEBIAN-12-CVE-2025-40139, ROOT-OS-DEBIAN-13-CVE-2025-40139, ROOT-OS-UBUNTU-2204-CVE-2025-40139, ROOT-OS-UBUNTU-2404-CVE-2025-40139, UBUNTU-CVE-2025-40139

## What is CVE-2025-40139?

CVE-2025-40139 is a high-severity use after free vulnerability in Linux, published on 12 Nov 2025. 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:

smc: Use __sk_dst_get() and dst_dev_rcu() in in smc_clc_prfx_set().

smc_clc_prfx_set() is called during connect() and not under RCU
nor RTNL.

Using sk_dst_get(sk)->dev could trigger UAF.

Let's use __sk_dst_get() and dev_dst_rcu() under rcu_read_lock()
after kernel_getsockname().

Note that the returned value of smc_clc_prfx_set() is not used
in the caller.

While at it, we change the 1st arg of smc_clc_prfx_set[46]_rcu()
not to touch dst there.

## Which versions are affected by CVE-2025-40139?


## How do I fix CVE-2025-40139?

Apply the vendor's patch.

## Is CVE-2025-40139 being exploited?

There is no known exploitation of CVE-2025-40139 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40139 and fix it if it is affected.

What it is: CVE-2025-40139 is a high-severity use after free vulnerability in Linux, published on 12 Nov 2025. 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-2025-40139 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-2025-40139/ (Markdown: https://insights.sbomify.com/CVE-2025-40139/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40139
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40139
- OSV: https://osv.dev/vulnerability/CVE-2025-40139

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40139/
Summaries are generated and may contain mistakes; the official description above is the record.