Server Message Block (SMB) is a protocol for sharing files, printers, serial ports, and communications abstractions, such as named pipes and mail slots between computers. Microsoft Windows operating systems utilize SMB server implementations.
Since SMB servers have a default Guest account, an unauthenticated, remote attacker attempting to login with an unrecognized account name will be logged in as "Guest." An exploit could allow the attacker to gain user privileges to view or modify files and gain control of the affected system.
Administrators are advised to disable all Guest accounts on local workstations and servers and domain controllers and to limit privileges to trusted users.