CVE-2026-53383ksmbd: reject non-VALID session in compound request branch
- 7.5HighCVSS base score
- 0.66%Exploitation in 30 daysEPSS · top 48% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By Linux
- 40 days later
· 40 days later
Published
- 29 days later
· 29 days later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| LinuxCNA (assigner) | 3.1 | High7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| NVDNVD · Analyzed | 3.1 | High7.5 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.66% · top 48% of all CVEs (12 Nov 2026)
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.5.
Affected products
- affected eb947403518ea3d93f6d89264bb1f5416bb0c7d0 – < 25ff12b82a376ff5c4583102a63d2456a6b9ebb9
- affected 854156d12caa9d36de1cf5f084591c7686cc8a9d – < fc578523a72cb8b329d32070b95898e81613cc3f
- affected 5005bcb4219156f1bf7587b185080ec1da08518e – < d2bbbb6c55812220fee5d801c275cc267ea3cbeb
- affected 5005bcb4219156f1bf7587b185080ec1da08518e – < 8f0302fb691537d33ec8f668565257ea9d340ffe
- affected 5005bcb4219156f1bf7587b185080ec1da08518e – < 7cad3ceaf679c55bc9946685dacafce78ce6b51a
- affected 5005bcb4219156f1bf7587b185080ec1da08518e – < 06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7
- affected 5005bcb4219156f1bf7587b185080ec1da08518e – < 5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4
- affected 5005bcb4219156f1bf7587b185080ec1da08518e – < 609ca17d869d04ba249e32cdcbf13c0b1c66f43c
- affected d1066c1b3663401cd23c0d6e60cdae750ce00c0f
- affected 5.15.121 – < 5.15.211
- affected 6.1.36 – < 6.1.177
- affected 6.3.10 – < 6.4
- affected 6.4
- unaffected < 6.4
- unaffected 5.15.211 – ≤ 5.15.*
- unaffected 6.1.177 – ≤ 6.1.*
- unaffected 6.6.144 – ≤ 6.6.*
- unaffected 6.12.95 – ≤ 6.12.*
- unaffected 6.18.37 – ≤ 6.18.*
- unaffected 7.0.14 – ≤ 7.0.*
- unaffected 7.1.2 – ≤ 7.1.*
- unaffected 7.2 – ≤ *
References
References8
- https://git.kernel.org/stable/c/25ff12b82a376ff5c4583102a63d2456a6b9ebb9 (opens in a new tab)
- https://git.kernel.org/stable/c/fc578523a72cb8b329d32070b95898e81613cc3f (opens in a new tab)
- https://git.kernel.org/stable/c/d2bbbb6c55812220fee5d801c275cc267ea3cbeb (opens in a new tab)
- https://git.kernel.org/stable/c/8f0302fb691537d33ec8f668565257ea9d340ffe (opens in a new tab)
- https://git.kernel.org/stable/c/7cad3ceaf679c55bc9946685dacafce78ce6b51a (opens in a new tab)
- https://git.kernel.org/stable/c/06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7 (opens in a new tab)
- https://git.kernel.org/stable/c/5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4 (opens in a new tab)
- https://git.kernel.org/stable/c/609ca17d869d04ba249e32cdcbf13c0b1c66f43c (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-45505 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-53383)Record last updated .