~/exploited / cve-2025-39964

CVE-2025-39964: Linux Kernel

According to CISA this vulnerability is already used in attacks (added on 18 September 2026).

Key facts

CVE	CVE-2025-39964
Vendor	Linux — Kernel
Vulnerability	Linux Kernel Race Condition Vulnerability
Added	18 September 2026
Deadline (US agencies)	21 September 2026
Ransomware campaigns	unknown

Description (CISA)

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.

Required action (CISA)

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.

What admins should do now

Affected? Check whether Linux Kernel is in use and which version runs (package manager, admin UI, --version).
Apply the vendor patch or workaround as soon as it exists. If that is not possible right away: restrict outside access (firewall, VPN, reverse proxy).
Review logs back to 18 September 2026: unusual logins, new files, unexpected processes, outbound connections.
If you suspect a compromise: isolate the system, rotate credentials, check the last backup from before the incident.

The deadline applies to US federal agencies. It is still a useful yardstick for everyone: when a flaw is attacked in the wild, waiting is not an option.

Sources

Data: CISA Known Exploited Vulnerabilities Catalog, as of 30 October 2026. No guarantee — always check the vendor's advisory.

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