CVE-2025-39964: in the CISA KEV catalogue
Linux Kernel Race Condition Vulnerability. CISA added CVE-2025-39964 to the Known Exploited Vulnerabilities catalogue on 2026-09-18 with a default due date of 2026-09-21. Known ransomware campaign use: Unknown. Forensic triage flag: Yes.
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 description)
- Vendor / product
- Linux Kernel
- CWE
- CWE-362
- 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.
- EPSS
- 1.6%, percentile 75 (scored 2026-11-03)
EPSS puts about 1.6 in 100 odds (1.6%) on exploitation activity being observed in the next 30 days. Its score is higher than or equal to that of 75% of scored CVEs. This is a model estimate about exploitation anywhere, not about your environment.
Vendor and reference links (from CISA)
- 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
Your own deadline under CISA BOD 26-04 depends on exposure, automatability and technical impact: work it out with the BOD 26-04 calculator.
Frequently asked questions
Is CVE-2025-39964 in the CISA KEV catalogue?
Yes. CISA added CVE-2025-39964 (Linux Kernel Race Condition Vulnerability) to the Known Exploited Vulnerabilities catalogue on 2026-09-18. CISA's default due date for it is 2026-09-21.
Is CVE-2025-39964 used in ransomware attacks?
CISA marks known ransomware campaign use as Unknown for CVE-2025-39964. That means CISA lacks confirmation, not that ransomware groups do not use it.
What should I do about CVE-2025-39964?
CISA's 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.
Sources
- CISA, Known Exploited Vulnerabilities Catalog (accessed 2026-11-03)
- FIRST, Exploit Prediction Scoring System (EPSS) (EPSS by FIRST; scores generated by Empirical Security)
- NVD record for CVE-2025-39964