{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-53383","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-06-09T07:44:35.401Z","datePublished":"2026-07-19T11:59:31.616Z","dateUpdated":"2026-08-17T04:50:33.785Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-17T04:50:33.785Z"},"descriptions":[{"lang":"en","value":"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 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$), the tree-connect then runs on that IN_PROGRESS session and\nreaches ksmbd_ipc_tree_connect_request(), which dereferences\nuser_name(sess->user) with sess->user == NULL (transport_ipc.c:687/701/704)\n-> remote NULL-pointer dereference and a kernel Oops that wedges the ksmbd\nworker for all clients.\n\nReject any non-first compound operation that lands on a session which is\nnot SMB2_SESSION_VALID, mirroring the validity the standalone lookup path\nenforces. SESSION_SETUP itself legitimately runs on an IN_PROGRESS session,\nbut it is never carried as a non-first compound operation, so multi-leg\nauthentication is unaffected by this check."}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:N - The bug is in ksmbd's SMB2 compound-request handler, reachable by any remote attacker who can send crafted SMB2 packets to TCP port 445 on a host running the in-kernel SMB server.\nAC:L - An attacker can reliably trigger the bug by sending a compound SMB2 request with SESSION_SETUP (NTLM Type-1 only) as the first operation and TREE_CONNECT (SessionId=0xFFFFFFFFFFFFFFFF, \\\\host\\IPC$) as the second; no special timing, memory layout, or victim state is required.\nPR:N - Exploitation requires only network access to ksmbd during the SMB2 authentication handshake, before sess->user is assigned; no Linux local account, capability, or prior authenticated OS session is needed.\nUI:N - No victim user action (opening files, mounting shares, clicking links) is required; the attacker triggers the crash solely by sending malicious SMB2 protocol traffic.\nS:U - The impact is a kernel oops and ksmbd worker disruption within the kernel/SMB server security authority; it does not cross a VM, container, or IOMMU boundary.\nC:N - The failure is a NULL pointer dereference on sess->user in ksmbd_ipc_tree_connect_request() when user_name(sess->user) is called with sess->user == NULL; this is a pure crash with no information disclosure.\nI:N - The bug causes a NULL pointer dereference only; there is no memory corruption, arbitrary write, or code-execution primitive—only a kernel fault.\nA:H - The NULL dereference causes a kernel oops that wedges the shared ksmbd-io workqueue worker, denying SMB service to all clients connected through that worker and potentially panicking the host if panic_on_oops is enabled."}]}],"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","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:*:*:*:*:*:*:*:*","versionStartIncluding":"6.4","versionEndExcluding":"6.18.37"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.4","versionEndExcluding":"7.0.14"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.4","versionEndExcluding":"7.1.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.4","versionEndExcluding":"7.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.3.10"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/25ff12b82a376ff5c4583102a63d2456a6b9ebb9"},{"url":"https://git.kernel.org/stable/c/fc578523a72cb8b329d32070b95898e81613cc3f"},{"url":"https://git.kernel.org/stable/c/d2bbbb6c55812220fee5d801c275cc267ea3cbeb"},{"url":"https://git.kernel.org/stable/c/8f0302fb691537d33ec8f668565257ea9d340ffe"},{"url":"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"}}}}