MajorExploited now Active exploitation

CVE-2025-39964: Linux Kernel Race Condition Vulnerability

CISA KEV · officialPublished Sep 18, 2026Risk 77/100

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. Vendor: Linux — Kernel Required Action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines. Due: 2026-09-21

Recommended action

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

CISA remediation due: 2026-09-21

Technical details

Vendor: Linux
Product: Kernel
Exploitation: active
Evidence: official

Evidence and sources

This record is attributed to CISA KEV. Exploitation status and remediation guidance are kept separate from the vulnerability's technical severity.

Open primary source