# CVE-2025-39964 — Linux **CISA KEV** > As of 2026-09-19, CVE-2025-39964 is a HIGH-severity vulnerability in Linux, CVSS v3.1 7.8, EPSS 1.2% (69.0th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2026-09-18), with a US federal remediation deadline of 2026-09-21. Threadlinqs Intelligence links 2 tracked threat campaigns to CVE-2025-39964, most recently “Debian Trixie kernel update DSA-6528-1 patches 1,000+ Linux kernel CVEs (privilege escalation, DoS, information leaks)”. **Last updated:** 2026-09-19 ## 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. The record classifies CVE-2025-39964 under weakness class [CWE-362](https://intel.threadlinqs.com/cwe/CWE-362). Its CVSS v3 base vector states that the flaw requires local access to the host, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 367 days ago. ## Severity and exploitation probability - **CVSS v3.1 base score:** 7.8 — HIGH (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`) - **EPSS (FIRST):** 1.2% probability of exploitation in the next 30 days, higher than 69.0% of all scored CVEs - **CISA KEV:** Listed since 2026-09-18, federal remediation deadline 2026-09-21 - **Threadlinqs priority:** 9/10 — CISA KEV-listed, which Threadlinqs floors at 9 - **Published:** 2025-10-13, last modified 2026-09-19 ## Is CVE-2025-39964 being exploited? CISA added CVE-2025-39964 to the Known Exploited Vulnerabilities catalog on 2026-09-18, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2026-09-21 under BOD 22-01. Weaponised exploit code for CVE-2025-39964 is publicly available. 3 public proof-of-concept repositories are tracked for this identifier. It currently carries a trending score of 40 in the Threadlinqs vulnerability feed. - [n1k0oowang/CVE-2025-39964_EXP](https://github.com/n1k0oowang/CVE-2025-39964_EXP) (github) - [suominen/CVE-2025-39964](https://github.com/suominen/CVE-2025-39964) (github) - [trickest/cve](https://github.com/trickest/cve/blob/main/2025/CVE-2025-39964.md) (trickest) ## Affected products and versions - [Linux](https://intel.threadlinqs.com/vendors/linux): Linux ## How to fix CVE-2025-39964 Because CVE-2025-39964 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2026-09-21. No vendor patch reference has been recorded for CVE-2025-39964 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise. ## Threat activity tracking CVE-2025-39964 2 tracked threats in the Threadlinqs corpus reference CVE-2025-39964, either in the campaign’s CVE list or as an indicator on the campaign record. - [Debian Trixie kernel update DSA-6528-1 patches 1,000+ Linux kernel CVEs (privilege escalation, DoS, information leaks)](https://intel.threadlinqs.com/threat/TL-2026-2849) — HIGH · 2026-09-29 - [CISA Flags Three Actively Exploited Linux Kernel Vulnerabilities: kTLS Receive-Path Disclosure/DoS, ebtables SNAT Privilege Escalation, and AF_ALG Race Condition (CVE-2025-39682, CVE-2026-53266, CVE-2025-39964)](https://intel.threadlinqs.com/threat/TL-2026-2582) — CRITICAL · 2026-09-19 ## Sources Enriched from CVE.org, FIRST EPSS, CISA KEV, GitHub Security Advisories, public proof-of-concept repositories. Last verified by Threadlinqs on 2026-10-10. **Other references** - [git.kernel.org](https://git.kernel.org/stable/c/0f28c4adbc4a97437874c9b669fd7958a8c6d6ce) - [git.kernel.org (e4c1ec11132ec466f7362a95f36a506ce4dc08c9)](https://git.kernel.org/stable/c/e4c1ec11132ec466f7362a95f36a506ce4dc08c9) - [git.kernel.org (1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8)](https://git.kernel.org/stable/c/1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8) - [git.kernel.org (7c4491b5644e3a3708f3dbd7591be0a570135b84)](https://git.kernel.org/stable/c/7c4491b5644e3a3708f3dbd7591be0a570135b84) - [git.kernel.org (9aee87da5572b3a14075f501752e209801160d3d)](https://git.kernel.org/stable/c/9aee87da5572b3a14075f501752e209801160d3d) _Showing 5 of 7 recorded references._ Canonical: https://intel.threadlinqs.com/cve/CVE-2025-39964 Full detection coverage and IOCs for threats exploiting CVE-2025-39964 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp