CVE-2026-64399
CriticalCVSS 9.8Exploitation Probability (EPSS)
Low risk39th percentile - higher than 39% of all known CVEs
Summary
In the Linux kernel ksmbd SMB server, the FSCTL_DUPLICATE_EXTENTS_TO_FILE function lacks write permission checks at the share and handle levels, allowing a client to overwrite destination file data even on a read-only share or with a FILE_WRITE_ATTRIBUTES handle.
Risk Assessment
An attacker can overwrite data in a destination file on a read-only SMB share, potentially leading to data loss or unauthorized file modification.
Recommendation
Apply the Linux kernel patch that adds KSMBD_TREE_CONN_FLAG_WRITABLE and FILE_WRITE_DATA permission checks in FSCTL_DUPLICATE_EXTENTS_TO_FILE and update your system to a version containing this fix.
Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: ksmbd: add permission checks for FSCTL_DUPLICATE_EXTENTS_TO_FILE The FSCTL_DUPLICATE_EXTENTS_TO_FILE arm of smb2_ioctl() overwrites the destination file's data via vfs_clone_file_range() with neither the share-level KSMBD_TREE_CONN_FLAG_WRITABLE check nor a per-handle fp->daccess check that the other write-bearing arms carry. A client can overwrite destination data on a read-only share, or from a handle opened with only FILE_WRITE_ATTRIBUTES (which still yields an FMODE_WRITE filp). FILE_WRITE_ATTRIBUTES-only destination handle overwrote the file's data via the clone. Add both checks, matching the FSCTL_SET_SPARSE permission fix; require FILE_WRITE_DATA since this writes data.