Check your EC2 security groups for inbound rules that allow unrestricted access (0.0.0.0/0 or ::/0) to TCP port 139 and UDP ports 137 and 138 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. These ports are used for NetBIOS name resolution (i.e. mapping a NetBIOS name to an IP address) by services such as File and Printer Sharing service running on Microsoft Windows Server OS.
Allowing unrestricted NetBIOS access can increase opportunities for malicious activity such as man-in-the-middle attacks (MITM), Denial of Service (DoS) attacks or BadTunnel exploits.
To determine if your EC2 security groups allow unrestricted NetBIOS access, perform the following:
To update your security groups inbound/ingress configuration in order to restrict NetBIOS access to specific entities (IP addresses, IP ranges, etc), perform the following: