# CVE-2025-39964: crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg

> CVE-2025-39964: crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg. CVSS 7.8 (CVSS 3.1), in CISA KEV.

Canonical: https://rewindex.com/cve/CVE-2025-39964
Last updated: 2026-10-19T21:10:00Z

- Published: 2025-10-13 13:48 UTC · Updated: 2026-10-19 21:10 UTC · Assigner: Linux
- CVSS: 7.8 (CVSS 3.1) · Severity: High · Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- EPSS: 1.6%, 75th percentile (scored 2026-10-25)
- CISA KEV: yes, added 2026-09-18, federal due date 2026-09-21, ransomware use: Unknown

## 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.

## CISA required action

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

## Affected vendors and products

- Linux: Linux
- Siemens: SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
- Siemens: SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
- Siemens: SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2025-39964)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2025-39964)
- [https://git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce](https://git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce)
- [https://git.kernel.org/stable/c/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285](https://git.kernel.org/stable/c/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285)
- [https://git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8](https://git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8)
- [https://git.kernel.org/stable/c/45bcf60fe49b37daab1acee57b27211ad1574042](https://git.kernel.org/stable/c/45bcf60fe49b37daab1acee57b27211ad1574042)
- [https://git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84](https://git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84)
- [https://git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d](https://git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d)
- [https://git.kernel.org/stable/c/e4c1ec11132ec466f7362a95f36a506ce4dc08c9](https://git.kernel.org/stable/c/e4c1ec11132ec466f7362a95f36a506ce4dc08c9)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2025-39964 · Markdown: https://rewindex.com/cve/CVE-2025-39964.md · JSON: https://rewindex.com/api/v1/cves/CVE-2025-39964 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:17:04.432Z