19 September 2026
Reference: CVE-2025-39964
1. What is being reported?
The Linux kernel had a problem where two data write actions could happen at the same time on a specific part of the system handling cryptographic operations. This could cause data to become mixed up or the system to behave unpredictably. The Linux developers have fixed this by preventing simultaneous writes.
2. What this means in plain English
If your organisation uses Linux servers or devices that perform cryptographic tasks, this flaw could lead to data corruption or system instability, potentially causing service interruptions or security risks.
3. Could this affect a small business?
Small businesses or charities using Linux-based servers, especially those handling encrypted data or running cloud services on Linux, could be affected. Those not using Linux systems or cryptographic features are unlikely to be impacted.
4. What to do now
- Check with your IT provider or software supplier if your Linux systems are affected by this vulnerability.
- Ensure that all Linux systems are updated with the latest security patches as recommended by the vendor.
- If you use cloud services running Linux, confirm that the provider has applied the necessary mitigations or consider alternatives if not.
- Review your systems for any unusual behaviour that might indicate exploitation and follow your incident response plan if needed.
5. Ask your IT provider
Can you confirm whether our Linux systems are affected by CVE-2025-39964 and if the latest security updates or mitigations have been applied?
6. Bottom line
Make sure your Linux systems are updated promptly to avoid risks from this actively exploited vulnerability.
Information based on CISA KEV, NVD and reputable security reporting.