AI description
Automated description summarized from trusted sources.
CVE-2026-53383 is a vulnerability identified in the Linux kernel, specifically within the ksmbd component. This flaw involves an issue with session validation and an out-of-bounds read. The vulnerability arises because the `smb2_check_user_session()` function, when handling compound requests that are not the first operation, reuses the session bound by the initial operation without fully re-checking its validity. This can lead to a situation where a non-first compound operation proceeds on a session that is not in a valid state, potentially resulting in a remote NULL-pointer dereference and a kernel Oops that can wedge the ksmbd worker for all clients.
- Description
- In the Linux kernel, the following vulnerability has been resolved: ksmbd: reject non-VALID session in compound request branch smb2_check_user_session() takes a shortcut for any operation that is not the first in a COMPOUND request: it reuses work->sess (the session bound by the first operation) and validates only the SessionId, then returns "valid". It never re-checks work->sess->state == SMB2_SESSION_VALID, and a SessionId of 0xFFFFFFFFFFFFFFFF (ULLONG_MAX, the MS-SMB2 related-operation value) skips even the id comparison. The standalone path (ksmbd_session_lookup_all() plus the SESSION_SETUP state machine) does enforce the VALID state; the compound branch bypasses all of it. A SESSION_SETUP carrying only an NTLM Type-1 (NtLmNegotiate) blob publishes a fresh SMB2_SESSION_IN_PROGRESS session whose sess->user is still NULL (->user is assigned later, by ntlm_authenticate()). Used as operation 1 of a COMPOUND with operation 2 = TREE_CONNECT (related, SessionId=ULLONG_MAX, \\host\IPC$), the tree-connect then runs on that IN_PROGRESS session and reaches ksmbd_ipc_tree_connect_request(), which dereferences user_name(sess->user) with sess->user == NULL (transport_ipc.c:687/701/704) -> remote NULL-pointer dereference and a kernel Oops that wedges the ksmbd worker for all clients. Reject any non-first compound operation that lands on a session which is not SMB2_SESSION_VALID, mirroring the validity the standalone lookup path enforces. SESSION_SETUP itself legitimately runs on an IN_PROGRESS session, but it is never carried as a non-first compound operation, so multi-leg authentication is unaffected by this check.
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- NVD status
- Received
CVSS 3.1
- Type
- Secondary
- Base score
- 7.5
- Impact score
- 3.6
- Exploitability score
- 3.9
- Vector string
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Severity
- HIGH
- Hype score
- Not currently trending