{ "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" } } } }