ksmbd: reject non-VALID session in compound request branch

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-53383
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-19 12:16:49 UTC
Updated2026-07-20 15:16:40 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.002270000 probability, percentile 0.134820000 (date 2026-07-20)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected eb947403518ea3d93f6d89264bb1f5416bb0c7d0 25ff12b82a376ff5c4583102a63d2456a6b9ebb9 git Not specified
CNA Linux Linux affected 854156d12caa9d36de1cf5f084591c7686cc8a9d fc578523a72cb8b329d32070b95898e81613cc3f git Not specified
CNA Linux Linux affected 5005bcb4219156f1bf7587b185080ec1da08518e d2bbbb6c55812220fee5d801c275cc267ea3cbeb git Not specified
CNA Linux Linux affected 5005bcb4219156f1bf7587b185080ec1da08518e 8f0302fb691537d33ec8f668565257ea9d340ffe git Not specified
CNA Linux Linux affected 5005bcb4219156f1bf7587b185080ec1da08518e 7cad3ceaf679c55bc9946685dacafce78ce6b51a git Not specified
CNA Linux Linux affected 5005bcb4219156f1bf7587b185080ec1da08518e 06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7 git Not specified
CNA Linux Linux affected 5005bcb4219156f1bf7587b185080ec1da08518e 5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4 git Not specified
CNA Linux Linux affected 5005bcb4219156f1bf7587b185080ec1da08518e 609ca17d869d04ba249e32cdcbf13c0b1c66f43c git Not specified
CNA Linux Linux affected d1066c1b3663401cd23c0d6e60cdae750ce00c0f git Not specified
CNA Linux Linux affected 5.15.121 5.15.211 semver Not specified
CNA Linux Linux affected 6.1.36 6.1.177 semver Not specified
CNA Linux Linux affected 6.3.10 6.4 semver Not specified
CNA Linux Linux affected 6.4 Not specified
CNA Linux Linux unaffected 6.4 semver Not specified
CNA Linux Linux unaffected 5.15.211 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.177 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.144 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.95 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.37 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.14 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1.2 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/8f0302fb691537d33ec8f668565257ea9d340ffe 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/25ff12b82a376ff5c4583102a63d2456a6b9ebb9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/609ca17d869d04ba249e32cdcbf13c0b1c66f43c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/fc578523a72cb8b329d32070b95898e81613cc3f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d2bbbb6c55812220fee5d801c275cc267ea3cbeb 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/7cad3ceaf679c55bc9946685dacafce78ce6b51a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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