{"id":"CVE-2026-53383","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: reject non-VALID session in compound request branch\n\nsmb2_check_user_session() takes a shortcut for any operation that is not\nthe first in a COMPOUND request: it…","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: reject non-VALID session in compound request branch\n\nsmb2_check_user_session() takes a shortcut for any operation that is not\nthe first in a COMPOUND request: it…","severity":"none","published":"2026-07-19","updated":"2026-07-19","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-53383","references":[{"url":"https://git.kernel.org/stable/c/06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/25ff12b82a376ff5c4583102a63d2456a6b9ebb9","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/609ca17d869d04ba249e32cdcbf13c0b1c66f43c","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/7cad3ceaf679c55bc9946685dacafce78ce6b51a","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/8f0302fb691537d33ec8f668565257ea9d340ffe","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/d2bbbb6c55812220fee5d801c275cc267ea3cbeb","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/fc578523a72cb8b329d32070b95898e81613cc3f","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"tags":["nvd"],"ingestedAt":"2026-07-19T16:31:24.396Z","epss":0.00664,"epssPercentile":0.49927,"slug":"CVE-2026-53383","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: reject non-VALID session in compound request branch\n\nsmb2_check_user_session() takes a shortcut for any operation that is not\nthe first in a COMPOUND request: it reuses work->sess (the session bound by\nthe first operation) and validates only the SessionId, then returns\n\"valid\". 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}