Linux Kernel ksmbd CVE-2026-31410

The affected component is ksmbd, the in-kernel SMB3 server introduced in Linux 5.15. The FS_OBJECT_ID_INFORMATION structure is part of the SMB2/3 protocol response for querying filesystem object identity metadata. The bug lies in ksmbd's implementation of this query: rather than using the superblock's UUID (sb->s_uuid) as the canonical volume identifier, the pre-fix code did not properly resolve the identifier, particularly for filesystems that do not populate s_uuid. The corrected code uses sb->s_uuid as the primary source and falls back to stfs.f_fsid obtained from vfs_statfs() for filesystems without a UUID. The CVSS vector (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) indicates a local attack surface with high availability impact. No CWE was assigned; the root cause class most closely resembles CWE-476 (NULL Pointer Dereference) or CWE-665 (Improper Initialization), inferred from the nature of the UUID fallback logic and the A:H impact without confidentiality loss. CPE data confirms the affected product as cpe:2.3:a:linux:linux.