# CVE-2025-40158: ipv6: use RCU in ip6_output()

> A use-after-free vulnerability in the Linux kernel IPv6 output path allows attackers to potentially execute code or cause a system crash.

- **Severity:** High 8.1 (`CVSS:3.1/AV:N/AC:H/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:** 12 Nov 2025
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-70025, BELL-CVE-2025-40158, DEBIAN-CVE-2025-40158, GHSA-4g43-pmw7-v27w, ROOT-OS-DEBIAN-11-CVE-2025-40158, ROOT-OS-DEBIAN-12-CVE-2025-40158, ROOT-OS-DEBIAN-13-CVE-2025-40158, ROOT-OS-UBUNTU-2204-CVE-2025-40158, ROOT-OS-UBUNTU-2404-CVE-2025-40158, UBUNTU-CVE-2025-40158

## What is CVE-2025-40158?

CVE-2025-40158 is a high-severity use after free vulnerability in Linux, published on 12 Nov 2025. 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:

ipv6: use RCU in ip6_output()

Use RCU in ip6_output() in order to use dst_dev_rcu() to prevent
possible UAF.

We can remove rcu_read_lock()/rcu_read_unlock() pairs
from ip6_finish_output2().

## Which versions are affected by CVE-2025-40158?


## How do I fix CVE-2025-40158?

Apply the vendor's patch.

## Is CVE-2025-40158 being exploited?

There is no known exploitation of CVE-2025-40158 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40158 and fix it if it is affected.

What it is: CVE-2025-40158 is a high-severity use after free vulnerability in Linux, published on 12 Nov 2025. 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-2025-40158 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-2025-40158/ (Markdown: https://insights.sbomify.com/CVE-2025-40158/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40158
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40158
- OSV: https://osv.dev/vulnerability/CVE-2025-40158

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40158/
Summaries are generated and may contain mistakes; the official description above is the record.