Check your EC2 security groups for inbound rules that allow unrestricted access (i.e. 0.0.0.0/0 or ::/0) to TCP port 445 and restrict access to only those IP addresses that require it in order to implement the principle of least privilege and reduce the possibility of a breach. Common Internet File System (CIFS) port 445 is used by client/server applications to provide shared access to files, printers and communications between network nodes directly over TCP (without NetBIOS) in Microsoft Windows Server 2003 and later. CIFS is based on the enhanced version of Server Message Block (SMB) protocol for internet/intranet file sharing, developed by Microsoft: https://goo.gl/VJyR8O.
Allowing unrestricted CIFS access can increase opportunities for malicious activity such as man-in-the-middle attacks (MITM), Denial of Service (DoS) attacks or the Windows Null Session Exploit.
To determine if your EC2 security groups allow unrestricted CIFS access, perform the following:
To update your security groups inbound/ingress configuration in order to restrict Common Internet File System (CIFS) access to specific entities (IP addresses, IP ranges and security groups), perform the following: