CVE-2026-53383ksmbd: reject non-VALID session in compound request branch
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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.
- CVSS
- 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Weakness (CWE)
- Not given
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Linux
- NVD analysis
- Analyzed
- Record last updated
- Aug 17, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Linux Linux linux:linux (from the name) | from eb947403518ea3d93f6d89264bb1f5416bb0c7d0 before 25ff12b82a376ff5c4583102a63d2456a6b9ebb9; from 854156d12caa9d36de1cf5f084591c7686cc8a9d before fc578523a72cb8b329d32070b95898e81613cc3f; from 5005bcb4219156f1bf7587b185080ec1da08518e before d2bbbb6c55812220fee5d801c275cc267ea3cbeb; 5005bcb4219156f1bf7587b185080ec1da08518e builds before 8f0302fb691537d33ec8f668565257ea9d340ffe; 5005bcb4219156f1bf7587b185080ec1da08518e builds before 7cad3ceaf679c55bc9946685dacafce78ce6b51a; 5005bcb4219156f1bf7587b185080ec1da08518e builds before 06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7; 5005bcb4219156f1bf7587b185080ec1da08518e builds before 5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4; 5005bcb4219156f1bf7587b185080ec1da08518e builds before 609ca17d869d04ba249e32cdcbf13c0b1c66f43c; and 4 more ranges | CNA record |
linux linux_kernel linux:linux_kernel | from 5.15.121 before 5.15.211; from 6.1.36 before 6.1.177; from 6.3.10 before 6.4; from 6.4.1 before 6.6.144; from 6.7 before 6.12.95; from 6.13 before 6.18.37; from 6.19 before 7.0.14; from 7.1 before 7.1.2; and 1 more ranges | NVD |
References
- https://git.kernel.org/stable/c/25ff12b82a376ff5c4583102a63d2456a6b9ebb9patch
- https://git.kernel.org/stable/c/fc578523a72cb8b329d32070b95898e81613cc3fpatch
- https://git.kernel.org/stable/c/d2bbbb6c55812220fee5d801c275cc267ea3cbebpatch
- https://git.kernel.org/stable/c/8f0302fb691537d33ec8f668565257ea9d340ffepatch
- https://git.kernel.org/stable/c/7cad3ceaf679c55bc9946685dacafce78ce6b51apatch
- https://git.kernel.org/stable/c/06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7patch
- https://git.kernel.org/stable/c/5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4patch
- https://git.kernel.org/stable/c/609ca17d869d04ba249e32cdcbf13c0b1c66f43cpatch
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.