Linux Kernel Ksmbd: Three SMB Vulnerabilities Disclosed Together on July 26, 2026
Three vulnerabilities in Linux kernel's Ksmbd component were disclosed together on July 26, 2026, all patched in a single kernel update.
Key findings
- Three Ksmbd vulnerabilities in the Linux kernel were disclosed on July 26, 2026.
- CVE-2026-64394 involves missing access checks for SMB2_SET_INFO.
- CVE-2026-64393 had incorrect credential handling in SMB2_SET_INFO operations.
- CVE-2026-64437 was a use-after-free flaw in SMB2_CLOSE and SMB2_CANCEL handling.
- All disclosed vulnerabilities were fixed in a single kernel update, version 6.9.3.
On July 26, 2026, a coordinated disclosure event brought to light three vulnerabilities in the Linux kernel's Ksmbd component, all addressed in a single, unified kernel update. These vulnerabilities, disclosed on the same day, highlight ongoing security efforts within the Linux kernel community and affect the SMB protocol implementation.
The vulnerabilities fall into distinct categories related to access control and memory management within the Ksmbd subsystem.
CVE-2026-64394 addresses an improper access control issue where checks for WRITE_DAC and WRITE_OWNER were missing for the SMB2_SET_INFO command. This could potentially allow unauthorized modifications to file security information.
CVE-2026-64393 relates to how Ksmbd handles security information. In this case, SMB2_SET_INFO handlers were calling VFS helpers with the credentials of the worker process rather than the original opener of the file. This could lead to incorrect permission evaluations for file operations.
CVE-2026-64437 is a use-after-free vulnerability that could occur when handling SMB2_CLOSE followed by SMB2_CANCEL. This memory corruption issue arises from how deferred file locks were managed, potentially leading to instability or crashes.
All three vulnerabilities were fixed in a single, unified kernel update, with reports indicating that version 6.9.3 contains these patches. Users of the Linux kernel are advised to update to the latest stable version to mitigate these risks. The coordinated disclosure of these Ksmbd vulnerabilities underscores the importance of timely patching for network file sharing services, as flaws in these components can have significant security implications.