The remote Samba server is affected by a signature downgrade vulnerability.
The version of Samba running on the remote host is 4.x prior to 4.2.14, 4.3.x prior to 4.3.11, or 4.4.x prior to 4.4.5. It is, therefore, affected by a flaw in libcli/smb/smbXcli_base.c that is triggered when handling SMB2 and SMB3 client connections. A man-in-the-middle attacker can exploit this, by injecting the SMB2_SESSION_FLAG_IS_GUEST or SMB2_SESSION_FLAG_IS_NULL flags, to downgrade the required signing for a client connection, allowing the attacker to spoof SMB2 and SMB3 servers.
Upgrade to Samba version 4.2.14 / 4.3.11 / 4.4.5 or later.