CVE-2026-64389ksmbd: validate NTLMv2 response before updating session key

Official description

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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/e589e997bddde0a6f45672dd871cba7b3ff28e17
• https://git.kernel.org/stable/c/a6a951416b55eaf51ea2742f7ba786f240e70137
• https://git.kernel.org/stable/c/f5d74c186bab26a5d5a025305e67edd0888aa34d
• https://git.kernel.org/stable/c/b56400364aed5c34d6e1a0b493081290a5328a9c
• https://git.kernel.org/stable/c/89ca7756d5566ba636bb9092cdbe57dab095e136
• https://git.kernel.org/stable/c/954d196bebb2b50151cb96454c72dc113b2af1ac