CVE-2025-39964 Linux Kernel: software flaw
In plain words: A mistake in the software that attackers have found a way to abuse. Depends on the product — see the description and the vendor advisory.
Confirmed exploited by CISA on · US federal patch deadline Sep 21, 2026
What to do
- Install Linux's security update for Kernel. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Turn on automatic updates for the operating system and for Office, PDF and archive apps.
- Be careful with unexpected attachments — documents, .zip/.rar files and shortcuts are common bait.
- Use a normal (non-admin) account day to day and keep built-in protection like Microsoft Defender on.
Who is affected
Could reach you. This one is aimed at devices or apps of the kind people own.
What's at risk: Your files, saved passwords and accounts. Many of these let a program that is already running gain full administrator control.
The details
- Official name
- Linux Kernel Race Condition Vulnerability
- Product
- Linux Kernel
- CISA description
- 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.
- Type of flaw
- Software flaw (CWE-362)
- Confirmed exploited
- Sep 18, 2026
- US federal patch deadline
- Sep 21, 2026
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Answering about CVE-2025-39964 ·
Questions about CVE-2025-39964
Is CVE-2025-39964 being exploited?
Yes. CISA added CVE-2025-39964 to its Known Exploited Vulnerabilities catalog on Sep 18, 2026, which means there is reliable evidence of real-world attacks.
How do I fix CVE-2025-39964?
Install Linux's security update for Kernel. If no update exists, follow the vendor's workaround or stop using the product until one ships. Turn on automatic updates for the operating system and for Office, PDF and archive apps.
Am I affected by CVE-2025-39964?
Only if you use Linux Kernel. This one is aimed at devices or apps of the kind people own.