CVE-2026-53383 - Vulnerability Details

Vendors	Products
Linux	Linux Kernel

Link	Providers
https://git.kernel.org/stable/c/06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7
https://git.kernel.org/stable/c/25ff12b82a376ff5c4583102a63d2456a6b9ebb9
https://git.kernel.org/stable/c/5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4
https://git.kernel.org/stable/c/609ca17d869d04ba249e32cdcbf13c0b1c66f43c
https://git.kernel.org/stable/c/7cad3ceaf679c55bc9946685dacafce78ce6b51a
https://git.kernel.org/stable/c/8f0302fb691537d33ec8f668565257ea9d340ffe
https://git.kernel.org/stable/c/d2bbbb6c55812220fee5d801c275cc267ea3cbeb
https://git.kernel.org/stable/c/fc578523a72cb8b329d32070b95898e81613cc3f

Type	Values Removed	Values Added
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.
Title		ksmbd: reject non-VALID session in compound request branch
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7 https://git.kernel.org/stable/c/25ff12b82a376ff5c4583102a63d2456a6b9ebb9 https://git.kernel.org/stable/c/5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4 https://git.kernel.org/stable/c/609ca17d869d04ba249e32cdcbf13c0b1c66f43c https://git.kernel.org/stable/c/7cad3ceaf679c55bc9946685dacafce78ce6b51a https://git.kernel.org/stable/c/8f0302fb691537d33ec8f668565257ea9d340ffe https://git.kernel.org/stable/c/d2bbbb6c55812220fee5d801c275cc267ea3cbeb https://git.kernel.org/stable/c/fc578523a72cb8b329d32070b95898e81613cc3f

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It never re-checks work->sess->state == SMB2_SESSION_VALID, and a\nSessionId of 0xFFFFFFFFFFFFFFFF (ULLONG_MAX, the MS-SMB2 related-operation\nvalue) skips even the id comparison. The standalone path\n(ksmbd_session_lookup_all() plus the SESSION_SETUP state machine) does\nenforce the VALID state; the compound branch bypasses all of it.\n\nA SESSION_SETUP carrying only an NTLM Type-1 (NtLmNegotiate) blob publishes\na fresh SMB2_SESSION_IN_PROGRESS session whose sess->user is still NULL\n(->user is assigned later, by ntlm_authenticate()). Used as operation 1 of\na COMPOUND with operation 2 = TREE_CONNECT (related, SessionId=ULLONG_MAX,\n\\\\host\\IPC$), the tree-connect then runs on that IN_PROGRESS session and\nreaches ksmbd_ipc_tree_connect_request(), which dereferences\nuser_name(sess->user) with sess->user == NULL (transport_ipc.c:687/701/704)\n-> remote NULL-pointer dereference and a kernel Oops that wedges the ksmbd\nworker for all clients.\n\nReject any non-first compound operation that lands on a session which is\nnot SMB2_SESSION_VALID, mirroring the validity the standalone lookup path\nenforces. SESSION_SETUP itself legitimately runs on an IN_PROGRESS session,\nbut it is never carried as a non-first compound operation, so multi-leg\nauthentication is unaffected by this check."}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["fs/smb/server/smb2pdu.c"], "versions": [{"version": "eb947403518ea3d93f6d89264bb1f5416bb0c7d0", "lessThan": "25ff12b82a376ff5c4583102a63d2456a6b9ebb9", "status": "affected", "versionType": "git"}, {"version": "854156d12caa9d36de1cf5f084591c7686cc8a9d", "lessThan": "fc578523a72cb8b329d32070b95898e81613cc3f", "status": "affected", "versionType": "git"}, {"version": "5005bcb4219156f1bf7587b185080ec1da08518e", "lessThan": "d2bbbb6c55812220fee5d801c275cc267ea3cbeb", "status": "affected", "versionType": "git"}, {"version": "5005bcb4219156f1bf7587b185080ec1da08518e", "lessThan": "8f0302fb691537d33ec8f668565257ea9d340ffe", "status": "affected", "versionType": "git"}, {"version": "5005bcb4219156f1bf7587b185080ec1da08518e", "lessThan": "7cad3ceaf679c55bc9946685dacafce78ce6b51a", "status": "affected", "versionType": "git"}, {"version": "5005bcb4219156f1bf7587b185080ec1da08518e", "lessThan": "06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7", "status": "affected", "versionType": "git"}, {"version": "5005bcb4219156f1bf7587b185080ec1da08518e", "lessThan": "5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4", "status": "affected", "versionType": "git"}, {"version": "5005bcb4219156f1bf7587b185080ec1da08518e", "lessThan": "609ca17d869d04ba249e32cdcbf13c0b1c66f43c", "status": "affected", "versionType": "git"}, {"version": "d1066c1b3663401cd23c0d6e60cdae750ce00c0f", "status": "affected", "versionType": "git"}, {"version": "5.15.121", "lessThan": "5.15.211", "status": "affected", "versionType": "semver"}, {"version": "6.1.36", "lessThan": "6.1.177", "status": "affected", "versionType": "semver"}, {"version": "6.3.10", "lessThan": "6.4", "status": "affected", "versionType": "semver"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["fs/smb/server/smb2pdu.c"], "versions": [{"version": "6.4", "status": "affected"}, {"version": "0", "lessThan": "6.4", "status": "unaffected", "versionType": "semver"}, {"version": "5.15.211", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.1.177", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.6.144", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.12.95", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver"}, {"version": "6.18.37", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.0.14", "lessThanOrEqual": "7.0.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.1.2", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.2-rc1", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15.121", "versionEndExcluding": "5.15.211"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.1.36", "versionEndExcluding": "6.1.177"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "6.6.144"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "6.12.95"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", 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"https://git.kernel.org/stable/c/7cad3ceaf679c55bc9946685dacafce78ce6b51a"}, {"url": "https://git.kernel.org/stable/c/06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7"}, {"url": "https://git.kernel.org/stable/c/5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4"}, {"url": "https://git.kernel.org/stable/c/609ca17d869d04ba249e32cdcbf13c0b1c66f43c"}], "title": "ksmbd: reject non-VALID session in compound request branch", "x_generator": {"engine": "bippy-1.2.0"}}}}

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