CVEs / CVE-2025-39964

CVE-2025-39964: Linux Kernel Race Condition Vulnerability

Known exploited in the CISA KEV catalog since 18 Sep 2026
medium 5.5 CVSS 3.1 (NVD)
EPSS 1.56% chance of exploitation in the next 30 days, higher than 75% of CVEs (30 Oct 2026)
Last changed at its sources 28 Oct 2026

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Summary

Linux Kernel contains a race condition vulnerability which allows concurrent writes to the same AF_ALG socket causing data to be unpredictably interleaved and creating inconsistencies in the socket's internal state.
CISA, Known Exploited Vulnerabilities catalog

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.
The CVE record, via NVD · published 13 Oct 2025 · NVD status: Analyzed

Affected and fixed versions

As stated by the CVE record (from the CNA)
Product	Affected	Fixed in
Linux Linux	from 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, before 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce	0f28c4adbc4a97437874c9b669fd7958a8c6d6ce
Linux Linux	from 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, before e4c1ec11132ec466f7362a95f36a506ce4dc08c9	e4c1ec11132ec466f7362a95f36a506ce4dc08c9
Linux Linux	from 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, before 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8	1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8
Linux Linux	from 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, before 7c4491b5644e3a3708f3dbd7591be0a570135b84	7c4491b5644e3a3708f3dbd7591be0a570135b84
Linux Linux	from 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, before 9aee87da5572b3a14075f501752e209801160d3d	9aee87da5572b3a14075f501752e209801160d3d
Linux Linux	from 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, before 45bcf60fe49b37daab1acee57b27211ad1574042	45bcf60fe49b37daab1acee57b27211ad1574042
Linux Linux	from 8ff590903d5fc7f5a0a988c38267a3d08e6393a2, before 1b34cbbf4f011a121ef7b2d7d6e6920a036d5285	1b34cbbf4f011a121ef7b2d7d6e6920a036d5285
Linux Linux	2.6.38	—
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP	from V3.1.6 onwards	—
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP	from V3.1.7 onwards	—
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP	from V3.1.6 onwards	—
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP	from V3.1.7 onwards	—
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP	from V3.1.6 onwards	—
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP	from V3.1.7 onwards	—

As stated by OSV
Product	Affected	Fixed in
Kernel (Linux)	from 2.6.38, before 5.10.245	5.10.245
Kernel (Linux)	from 5.11.0, before 5.15.194	5.15.194
Kernel (Linux)	from 5.16.0, before 6.1.154	6.1.154
Kernel (Linux)	from 6.2.0, before 6.6.108	6.6.108
Kernel (Linux)	from 6.7.0, before 6.12.49	6.12.49
Kernel (Linux)	from 6.13.0, before 6.16.9	6.16.9

Exploitation

In CISA KEV since	18 Sep 2026
Due date for US federal agencies	21 Sep 2026
Used in ransomware campaigns	Unknown
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.

Severity

CVSS 3.1	5.5 medium `CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H` Scored by NVD
Weakness	CWE-362

References

CVE-2025-39964 on NVD
CVE-2025-39964 in the CISA KEV catalog
https://git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce (cited by CISA)
https://git.kernel.org/stable/c/e4c1ec11132ec466f7362a95f36a506ce4dc08c9 (cited by CISA)
https://git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8 (cited by CISA)
https://git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84 (cited by CISA)
https://git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d (cited by CISA)
https://git.kernel.org/stable/c/45bcf60fe49b37daab1acee57b27211ad1574042 (cited by CISA)
https://git.kernel.org/stable/c/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285 (cited by CISA)
https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk (cited by CISA)
https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk (cited by CISA)
CVE-2025-39964 on OSV
https://git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce Patch
https://git.kernel.org/stable/c/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285 Patch
https://git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8 Patch
https://git.kernel.org/stable/c/45bcf60fe49b37daab1acee57b27211ad1574042 Patch
https://git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84 Patch
https://git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d Patch
https://git.kernel.org/stable/c/e4c1ec11132ec466f7362a95f36a506ce4dc08c9 Patch
https://cert-portal.siemens.com/productcert/html/ssa-019113.html Third Party Advisory
https://cert-portal.siemens.com/productcert/html/ssa-457936.html Third Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-39964 US Government Resource

Sources

Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.

This product uses data from the NVD API but is not endorsed or certified by the NVD.