CVE-2026-53383 (GCVE-0-2026-53383)

Vulnerability from cvelistv5 – Published: 2026-07-19 11:59 – Updated: 2026-08-17 04:50
VLAI
Title
ksmbd: reject non-VALID session in compound request branch
Summary
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.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: eb947403518ea3d93f6d89264bb1f5416bb0c7d0 , < 25ff12b82a376ff5c4583102a63d2456a6b9ebb9 (git)
Affected: 854156d12caa9d36de1cf5f084591c7686cc8a9d , < fc578523a72cb8b329d32070b95898e81613cc3f (git)
Affected: 5005bcb4219156f1bf7587b185080ec1da08518e , < d2bbbb6c55812220fee5d801c275cc267ea3cbeb (git)
Affected: 5005bcb4219156f1bf7587b185080ec1da08518e , < 8f0302fb691537d33ec8f668565257ea9d340ffe (git)
Affected: 5005bcb4219156f1bf7587b185080ec1da08518e , < 7cad3ceaf679c55bc9946685dacafce78ce6b51a (git)
Affected: 5005bcb4219156f1bf7587b185080ec1da08518e , < 06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7 (git)
Affected: 5005bcb4219156f1bf7587b185080ec1da08518e , < 5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4 (git)
Affected: 5005bcb4219156f1bf7587b185080ec1da08518e , < 609ca17d869d04ba249e32cdcbf13c0b1c66f43c (git)
Affected: d1066c1b3663401cd23c0d6e60cdae750ce00c0f (git)
Affected: 5.15.121 , < 5.15.211 (semver)
Affected: 6.1.36 , < 6.1.177 (semver)
Affected: 6.3.10 , < 6.4 (semver)
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Linux Linux Affected: 6.4
Unaffected: 0 , < 6.4 (semver)
Unaffected: 5.15.211 , ≤ 5.15.* (semver)
Unaffected: 6.1.177 , ≤ 6.1.* (semver)
Unaffected: 6.6.144 , ≤ 6.6.* (semver)
Unaffected: 6.12.95 , ≤ 6.12.* (semver)
Unaffected: 6.18.37 , ≤ 6.18.* (semver)
Unaffected: 7.0.14 , ≤ 7.0.* (semver)
Unaffected: 7.1.2 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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          "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-\u003esess (the session bound by\nthe first operation) and validates only the SessionId, then returns\n\"valid\". It never re-checks work-\u003esess-\u003estate == 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-\u003euser is still NULL\n(-\u003euser 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-\u003euser) with sess-\u003euser == NULL (transport_ipc.c:687/701/704)\n-\u003e 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."
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                    "versionStartIncluding": "6.3.10",
                    "vulnerable": true
                  },
                  {
                    "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                    "matchCriteriaId": "1FB20250-D599-4124-9B31-4ACBD815386B",
                    "versionEndExcluding": "6.6.144",
                    "versionStartIncluding": "6.4.1",
                    "vulnerable": true
                  },
                  {
                    "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                    "versionStartIncluding": "6.7",
                    "vulnerable": true
                  },
                  {
                    "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                    "matchCriteriaId": "E08ACB05-518A-4D61-A6C4-268D1BB6BF46",
                    "versionEndExcluding": "6.18.37",
                    "versionStartIncluding": "6.13",
                    "vulnerable": true
                  },
                  {
                    "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                    "matchCriteriaId": "6241DF06-E6F3-4B61-B5A2-A60F2AE5B982",
                    "versionEndExcluding": "7.0.14",
                    "versionStartIncluding": "6.19",
                    "vulnerable": true
                  },
                  {
                    "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                    "matchCriteriaId": "C18FAA06-B61A-4036-A12D-F06F5135E64B",
                    "versionEndExcluding": "7.1.2",
                    "versionStartIncluding": "7.1",
                    "vulnerable": true
                  },
                  {
                    "criteria": "cpe:2.3:o:linux:linux_kernel:6.4:-:*:*:*:*:*:*",
                    "matchCriteriaId": "DE0B0BF6-0EEF-4FAD-927D-7A0DD77BEE75",
                    "vulnerable": true
                  }
                ],
                "negate": false,
                "operator": "OR"
              }
            ]
          }
        ],
        "cveTags": [],
        "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-\u003esess (the session bound by\nthe first operation) and validates only the SessionId, then returns\n\"valid\". It never re-checks work-\u003esess-\u003estate == 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-\u003euser is still NULL\n(-\u003euser 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-\u003euser) with sess-\u003euser == NULL (transport_ipc.c:687/701/704)\n-\u003e 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."
          }
        ],
        "id": "CVE-2026-53383",
        "lastModified": "2026-08-17T05:17:12.240",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 7.5,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "NONE",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 3.9,
              "impactScore": 3.6,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-07-19T12:16:49.117",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/06e1f05a1dbe8bbd054c0927b17fc0a61cc8bef7"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/25ff12b82a376ff5c4583102a63d2456a6b9ebb9"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/5f983b864d3d473ac533b2f4f44a1bbe5dcbccf4"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/609ca17d869d04ba249e32cdcbf13c0b1c66f43c"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/7cad3ceaf679c55bc9946685dacafce78ce6b51a"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/8f0302fb691537d33ec8f668565257ea9d340ffe"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/d2bbbb6c55812220fee5d801c275cc267ea3cbeb"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "tags": [
              "Patch"
            ],
            "url": "https://git.kernel.org/stable/c/fc578523a72cb8b329d32070b95898e81613cc3f"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Analyzed",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-476"
              }
            ],
            "source": "nvd@nist.gov",
            "type": "Primary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-07-21T08:06:48+00:00",
      "cve": "CVE-2026-53383",
      "id": "CVE-2026-53383",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_not_affected": "275",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ksmbd: reject non-VALID session in compound request branch",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-53383.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-08-02T16:37:23Z",
      "cve": "CVE-2026-53383",
      "id": "CVE-2026-53383",
      "initial_release_date": "2026-07-19T17:36:14Z",
      "product_status:known_not_affected": "298",
      "product_status:recommended": "4",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-53383",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-53383.json",
      "version": "5"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.