Critical [CVE-2026-68457] use opener credentials for FSCTL mutations

In the Linux kernel, the following vulnerability has been resolved: ksmbd: use opener credentials for FSCTL mutations SET_SPARSE, SET_ZERO_DATA and SET_COMPRESSION operate on an open SMB handle but call VFS xattr, fallocate or fileattr helpers with the current ksmbd worker credentials.

Those helpers can revalidate inode permissions, ownership and LSM policy independently of the SMB handle access mask. Run each operation with the credentials captured in the target file when the handle was opened.

Keep credential handling local to these single-file FSCTLs rather than applying session credentials to the complete IOCTL handler, which also contains handle-less and multi-handle operations. This vulnerability allows certain file system control (FSCTL) operations, specifically SET_SPARSE, SET_ZERO_DATA, and SET_COMPRESSION, to use incorrect credentials.

Consequently, these operations can bypass the security checks established when the file was initially opened. This could enable a local attacker to perform unauthorized modifications to files, circumventing intended access restrictions.

Red Hat severity: Important — CVSS 9.1 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H). Weakness: CWE-270.

Red Hat lists Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9 as not affected.