Overview
CVE-2025-39964 has been added to the CISA Known Exploited Vulnerabilities catalog. Published on October 13, 2025. Threat actors are actively exploiting this vulnerability in real-world attacks.
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.
Threat Intelligence
| Metric | Value |
|---|---|
| CVE ID | CVE-2025-39964 |
| Severity | HIGH |
| CVSS Score | 0.0/10 |
| CISA KEV | ✅ Yes — Actively Exploited |
| KEV Date Added | September 18, 2026 |
| Remediation Deadline | September 21, 2026 |
| EPSS Score | 0.3% exploit probability |
| EPSS Percentile | Top 100% of all CVEs |
Why This Matters
This vulnerability has been added to the CISA Known Exploited Vulnerabilities (KEV) catalog, which means threat actors are actively exploiting it in real-world attacks.
Federal agencies are required to remediate by September 21, 2026. All organizations should treat this deadline as a strong recommendation.
CISA 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
Recommended Actions
- Verify exposure — Determine if your environment uses the affected software.
- Apply patches — Update to the latest version as soon as a fix is available.
- Monitor for compromise — Check logs for unusual activity.
- Meet the deadline — CISA recommends remediation by September 21, 2026.
References
CVE data aggregated from the National Vulnerability Database (NVD), CISA Known Exploited Vulnerabilities catalog, and FIRST EPSS. Analysis updated as new intelligence becomes available. Last updated: 2026-09-18.