CVE-2025-39964

crypto: af_alg - Disallow concurrent writes in af_alg_sendmsg

MEDIUM

5.5

CVSS Score

Published: October 13, 2025 at 01:48 PM UTC

Updated: October 19, 2026 at 09:10 PM UTC

4 products affected across 2 vendorsLinux KernelSIMATIC S7-1500 CPU 1518-4 Pn /dp MFP FirmwareSIMATIC S7-1500 CPU 1518F 4 Pn /dp MFP Firmware· also runs on 2 platforms

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Severity

MEDIUM5.5

Exploitation

CISA KEV

Exploit prediction

EPSS 2%

SSVC

Active

Actively Exploited

CISA Known Exploited Vulnerabilities (KEV) Catalog

EPSS Score1.6%

EPSS (Exploit Prediction Scoring System) estimates a 1.6% chance this CVE is exploited in the wild within the next 30 days — higher than 75% of all CVEs. It complements CVSS: a high EPSS on a mid-severity CVE can still be urgent.

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.

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.

Ransomware Use

Unknown

Added to KEV

Sep 18, 2026

Remediation Due

Sep 21, 2026

41 days overdue

Notes

This vulnerability affects an open-source component, third-party library, protocol, or proprietary implementation that could be used by different products. For more information, please see:

https://git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce

https://git.kernel.org/stable/c/e4c1ec11132ec466f7362a95f36a506ce4dc08c9

https://git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8

https://git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84

https://git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d

https://git.kernel.org/stable/c/45bcf60fe49b37daab1acee57b27211ad1574042

https://git.kernel.org/stable/c/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285

BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk

Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk

https://nvd.nist.gov/vuln/detail/CVE-2025-39964

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Linux Kernel · Linux

95%

2.6.38 ≤ v < 5.10.2455.11 ≤ v < 5.15.1945.16 ≤ v < 6.1.1546.13 ≤ v < 6.16.96.2 ≤ v < 6.6.1086.7 ≤ v < 6.12.496.17 6.17 rc1 6.17 rc2 6.17 rc3 6.17 rc4 6.17 rc5 6.17 rc68ff590903d5fc7f5a0a988c38267a3d08e6393a2

Vendor states this is fixed in 0f28c4adbc4a97437874c9b669fd7958a8c6d6ce (fixed)

Vendor states this is fixed in 1b34cbbf4f011a121ef7b2d7d6e6920a036d5285 (fixed)

Vendor states this is fixed in 1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8 (fixed)

Vendor states this is fixed in 45bcf60fe49b37daab1acee57b27211ad1574042 (fixed)

Vendor states this is fixed in 7c4491b5644e3a3708f3dbd7591be0a570135b84 (fixed)

Vendor states this is fixed in 9aee87da5572b3a14075f501752e209801160d3d (fixed)

Vendor states this is fixed in e4c1ec11132ec466f7362a95f36a506ce4dc08c9 (fixed)

Vendor states this is fixed in 2.6.38 (unaffected)

Vendor states this is fixed in 5.10.245 (unaffected)

Vendor states this is fixed in 5.15.194 (unaffected)

Vendor states this is fixed in 6.1.154 (unaffected)

Vendor states this is fixed in 6.12.49 (unaffected)