CVE-2025-39964: Linux Kernel race condition in af_alg_sendmsg

CVE-2025-39964 · Severity: critical · CVSS 3.3 · Exploited in the wild · Published 2025-10-13

A race condition flaw in the Linux Kernel is being actively exploited by attackers to compromise systems. This vulnerability allows attackers to gain complete control of affected systems, making it a critical target for organizations to patch immediately. Federal agencies are required to prioritize fixing this issue on any externally facing infrastructure under Binding Operational Directive 26-04.

Technologies: Linux Kernel, 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. Vendors: Linux, Siemens.

Quick answers

Is CVE-2025-39964 exploited in the wild?
Yes. CVE-2025-39964 is known to be exploited in the wild, first recorded on 18 September 2026. Treat it as urgent.
How severe is CVE-2025-39964?
Critical severity, with a CVSS score of 3.3, published 13 October 2025.
Which products and versions are affected?
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.6; Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.6; Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.6.
Is there a fix for CVE-2025-39964?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2025-39964 attacked?
It is attacked over the network or with local access, in an operating system.
Am I affected by CVE-2025-39964?
Check whether you run Linux Kernel, Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP, Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

CVE-2025-39964 is a race condition vulnerability in the Linux Kernel that has been confirmed as actively exploited in the wild and added to CISA's Known Exploited Vulnerabilities Catalog. Race condition vulnerabilities typically arise from improper synchronization of concurrent operations, allowing attackers to exploit timing windows to corrupt kernel state or bypass security controls. The vulnerability is reachable over the network or through local access depending on the specific kernel subsystem affected. Successful exploitation grants total control of the affected system, enabling arbitrary code execution at kernel privilege level. Organizations should apply vendor-supplied kernel patches immediately, particularly on publicly exposed systems. CISA provides detailed mitigation guidance and monitoring recommendations for this vulnerability.

Affected products

  • Linux Kernel <UNKNOWN>

Timeline

  • 2026-09-18: disclosed
  • 2026-09-18: kev added

References

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