{"id":"CVE-2026-64389","summary":"ksmbd: validate NTLMv2 response before updating session key","details":"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.","modified":"2026-07-28T04:02:47.796691080Z","published":"2026-07-25T08:50:36.817Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64389.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/89ca7756d5566ba636bb9092cdbe57dab095e136"},{"type":"WEB","url":"https://git.kernel.org/stable/c/954d196bebb2b50151cb96454c72dc113b2af1ac"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b56400364aed5c34d6e1a0b493081290a5328a9c"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64389.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-64389"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9"},{"fixed":"b56400364aed5c34d6e1a0b493081290a5328a9c"},{"fixed":"89ca7756d5566ba636bb9092cdbe57dab095e136"},{"fixed":"954d196bebb2b50151cb96454c72dc113b2af1ac"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64389.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"5.15.0"},{"fixed":"6.18.40"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.4"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64389.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:H"}]}