CVE-2025-39964

CVE-2025-39964 is a high-severity vulnerability in Linux Linux Kernel with a CVSS 3.x base score of 7.8. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2026-09-18). The underlying weakness is classified as CWE-362.

Key facts

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.

Frequently asked questions

What is CVE-2025-39964?
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.
How severe is CVE-2025-39964?
CVE-2025-39964 has a CVSS 3.x base score of 7.8, rated high severity. It is exploitable over local access with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2025-39964 being actively exploited?
Yes. CVE-2025-39964 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2026-09-18, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2025-39964?
CVE-2025-39964 primarily affects Linux Linux Kernel. In total, 9 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2025-39964?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2025-39964 have an EU (EUVD) identifier?
Yes. CVE-2025-39964 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-34068.
When was CVE-2025-39964 published?
CVE-2025-39964 was published on 2025-10-13 and last updated on 2026-09-19.

References

Affected products (9)

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