CVE-2026-64389

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 Software

References

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