CVE-2026-64389 (GCVE-0-2026-64389)
Vulnerability from cvelistv5
Published
2026-07-25 08:50
Modified
2026-10-21 12:43
Severity ?
8.2 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: validate NTLMv2 response before updating session key ksmbd_auth_ntlmv2() derives the NTLMv2 session key into sess->sess_key before it verifies the NTLMv2 response. ksmbd_decode_ntlmssp_auth_blob() then continues into KEY_XCH even when ksmbd_auth_ntlmv2() failed. With SMB3 multichannel binding, the failed authentication operates on an existing session and the session setup error path does not expire binding sessions. A client can send a binding session setup with a bad NT proof and KEY_XCH and still modify sess->sess_key before STATUS_LOGON_FAILURE is returned. Relevant path: smb2_sess_setup() -> conn->binding = true -> ntlm_authenticate() -> session_user() -> ksmbd_decode_ntlmssp_auth_blob() -> ksmbd_auth_ntlmv2() -> calc_ntlmv2_hash() -> hmac_md5_usingrawkey(..., sess->sess_key) -> crypto_memneq() returns mismatch -> KEY_XCH arc4_crypt(..., sess->sess_key, ...) -> out_err without expiring the binding session Derive the base session key into a local buffer and copy it to sess->sess_key only after the proof matches. Return immediately on authentication failure so KEY_XCH is only processed after successful authentication.
References
Impacted products
Vendor Product Version
Linux Linux Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
Version: e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9
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          "programFiles": [
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: validate NTLMv2 response before updating session key\n\nksmbd_auth_ntlmv2() derives the NTLMv2 session key into\nsess-\u003esess_key before it verifies the NTLMv2 response.\nksmbd_decode_ntlmssp_auth_blob() then continues into KEY_XCH even\nwhen ksmbd_auth_ntlmv2() failed.\n\nWith SMB3 multichannel binding, the failed authentication operates on\nan existing session and the session setup error path does not expire\nbinding sessions. A client can send a binding session setup with a\nbad NT proof and KEY_XCH and still modify sess-\u003esess_key before\nSTATUS_LOGON_FAILURE is returned.\n\nRelevant path:\n\n  smb2_sess_setup()\n    -\u003e conn-\u003ebinding = true\n    -\u003e ntlm_authenticate()\n       -\u003e session_user()\n       -\u003e ksmbd_decode_ntlmssp_auth_blob()\n          -\u003e ksmbd_auth_ntlmv2()\n             -\u003e calc_ntlmv2_hash()\n             -\u003e hmac_md5_usingrawkey(..., sess-\u003esess_key)\n             -\u003e crypto_memneq() returns mismatch\n          -\u003e KEY_XCH arc4_crypt(..., sess-\u003esess_key, ...)\n    -\u003e out_err without expiring the binding session\n\nDerive the base session key into a local buffer and copy it to\nsess-\u003esess_key only after the proof matches. Return immediately on\nauthentication failure so KEY_XCH is only processed after successful\nauthentication."
        }
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            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H",
            "version": "3.1"
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          "scenarios": [
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              "value": "AV:N - The vulnerable NTLMv2 authentication path is reached remotely through ksmbd SESSION_SETUP requests over SMB on TCP/445.\nAC:L - An attacker can deterministically trigger the key overwrite using a malformed multichannel binding request with KEY_XCH; no race or condition beyond attacker control is required.\nPR:N - The overwrite occurs before NTLMv2 proof validation, and the affected code does not verify the binding request signature, so valid credentials or an authenticated attacker session are unnecessary.\nUI:N - No victim action is required beyond an active SMB session, which can belong to an automated client or service.\nS:U - The corrupted session state and resulting effects remain within the ksmbd server and host kernel security authority.\nC:N - The bounded session-key overwrite does not disclose the prior key, kernel memory, or protected SMB data.\nI:L - The attacker can modify an established session\u0027s security-critical key state, but cannot reliably select the resulting key or obtain an arbitrary memory or file-write primitive.\nA:H - Repeated unauthenticated key corruption can desynchronize signing-key derivation and render targeted multichannel binding or session recovery unusable, causing complete loss of the affected SMB session in dependent deployments."
            }
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      "providerMetadata": {
        "dateUpdated": "2026-10-21T12:43:20.010Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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      "references": [
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          "url": "https://git.kernel.org/stable/c/a6a951416b55eaf51ea2742f7ba786f240e70137"
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          "url": "https://git.kernel.org/stable/c/f5d74c186bab26a5d5a025305e67edd0888aa34d"
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        {
          "url": "https://git.kernel.org/stable/c/89ca7756d5566ba636bb9092cdbe57dab095e136"
        },
        {
          "url": "https://git.kernel.org/stable/c/954d196bebb2b50151cb96454c72dc113b2af1ac"
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      "title": "ksmbd: validate NTLMv2 response before updating session key",
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64389",
    "datePublished": "2026-07-25T08:50:36.817Z",
    "dateReserved": "2026-07-19T15:36:31.785Z",
    "dateUpdated": "2026-10-21T12:43:20.010Z",
    "state": "PUBLISHED"
  },
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}


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