CVE-2025-39964: Linux Kernel Race Condition Vulnerability

What it is

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.

What to do

Schedule the vendor fix into this week’s change window, prioritising internet-facing and business-critical systems. Confirm the fix is applied everywhere, not just where it was easy.

Priority

This week: Schedule into this week’s change window.

Severity (CVSS)

7.8 high

CISA assessment (SSVC)

actively exploited; needs manual effort per target; total control of the affected system

Exploit probability (EPSS, 30 days)

1.3%, higher than 69% of all CVEs

Added to CISA KEV

18 September 2026

CISA fix-by date

21 September 2026 (US federal agencies; a sensible deadline for everyone)

Ransomware use

Not known

Weakness

CWE-362

References

• NIST NVD entry
• CISA KEV entry
• git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce
• git.kernel.org/stable/c/1b34cbbf4f011a121ef7b2d7d6e6920a036d5285
• git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8
• git.kernel.org/stable/c/45bcf60fe49b37daab1acee57b27211ad1574042
• git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84
• git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d

Sources: CISA Known Exploited Vulnerabilities · FIRST Exploit Prediction Scoring System (EPSS) · NIST National Vulnerability Database · CISA Vulnrichment (SSVC), via the CVE Program. This product uses data from the NVD API but is not endorsed or certified by the NVD. Summaries are machine-written from CISA’s description; treat the vendor’s advisory as the authority for fixes.