CVE-2025-39943
A critical flaw in the Linux kernel’s SMB server can let attackers read memory and crash the system. The bug is triggered by malformed SMB data and is fixed by a kernel patch that validates the data fields.
An official fix is available, so this entry is kept for 30 days and then removed automatically.
Who is affected
Linux kernel 5.15 and 6.17 (and any other versions that include the ksmbd smbdirect component).
Real-world impact
An attacker who can send crafted SMB packets to the target can read sensitive data from memory and cause a denial‑of‑service crash, potentially disrupting services.
Why this severity
The CVSS score of 9.4 reflects that the flaw can be exploited over the network without authentication, giving the attacker high confidentiality and availability impact while requiring only low effort.
What to do about it
- 01Upgrade the Linux kernel to a version that includes the ksmbd smbdirect patch (e.g., the latest 5.15.x or 6.17.x release).
- 02Reboot the system to load the updated kernel.
NVD-referenced vendor advisory
Timeline
- Oct 4, 2025 · Oct 4, 2025PublishedDisclosed and added to the National Vulnerability Database.
- Jul 30, 2026 · 6d agoAdvisory updatedThe NVD record was last revised.
- Jul 30, 2026 · 6d agoOfficial fix availableA vendor patch or mitigation now exists — see the remediation steps above.