# CVE-2025-39964: Linux Kernel Race Condition

> Concurrent writes to an af_alg socket can cause data interleaving and internal state inconsistencies, potentially leading to data corruption or denial of service.

- **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:** Yes, since 18 Sep 2026 (CISA KEV)
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 13 Oct 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-68460, AZL-76437, BELL-CVE-2025-39964, DEBIAN-CVE-2025-39964, GHSA-wr5g-mfhw-rpfj, ROOT-OS-DEBIAN-11-CVE-2025-39964, ROOT-OS-DEBIAN-12-CVE-2025-39964, ROOT-OS-DEBIAN-13-CVE-2025-39964, ROOT-OS-UBUNTU-2204-CVE-2025-39964, ROOT-OS-UBUNTU-2404-CVE-2025-39964, UBUNTU-CVE-2025-39964

## What is CVE-2025-39964?

CVE-2025-39964 is a high-severity vulnerability in Linux kernel, published on 13 Oct 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:

crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg

Issuing two writes to the same af_alg socket is bogus as the
data will be interleaved in an unpredictable fashion.  Furthermore,
concurrent writes may create inconsistencies in the internal
socket state.

Disallow this by adding a new ctx->write field that indiciates
exclusive ownership for writing.

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2025-39964?

It affects 3 products.


Products: Linux kernel, Siemens Simatic S7-1500 Cpu 1518-4 Pn\/Dp Mfp Firmware, Siemens Simatic S7-1500 Cpu 1518f-4 Pn\/Dp Mfp Firmware.

## How do I fix CVE-2025-39964?

Apply the vendor's patch. US federal agencies must fix it by 21 Sep 2026.

## Is CVE-2025-39964 being exploited?

Yes. Attackers have exploited CVE-2025-39964 in the wild since at least 18 Sep 2026.

Public exploit code:

- CVE-2025-39964 EXP (github_poc): https://github.com/n1k0oowang/CVE-2025-39964_EXP
- Tracking CVE-2025-39964, the Linux kernel AF_ALG concurrent-write race (github_poc): https://github.com/suominen/CVE-2025-39964

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-39964 and fix it if it is affected.

What it is: CVE-2025-39964 is a high-severity vulnerability in Linux kernel, published on 13 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2025-39964 in the wild since at least 18 Sep 2026.

Affected product: Linux kernel. 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-2025-39964/ (Markdown: https://insights.sbomify.com/CVE-2025-39964/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39964
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39964
- OSV: https://osv.dev/vulnerability/CVE-2025-39964

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39964/
Summaries are generated and may contain mistakes; the official description above is the record.