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. 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 366 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 (github)
- suominen/CVE-2025-39964 (github)
- trickest/cve (trickest)
Affected products and versions
- 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) — 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) — 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 .
Other references
- git.kernel.org
- git.kernel.org (e4c1ec11132ec466f7362a95f36a506ce4dc08c9)
- git.kernel.org (1f323a48e9b5ebfe6dc7d130fdf5c3c0e92a07c8)
- git.kernel.org (7c4491b5644e3a3708f3dbd7591be0a570135b84)
- git.kernel.org (9aee87da5572b3a14075f501752e209801160d3d)
Showing 5 of 7 recorded references.