Check your EC2 security groups for inbound rules that allow unrestricted access (i.e. 0.0.0.0/0 or ::/0) to TCP port 3389 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. TCP port 3389 is used for secure remote GUI login to Microsoft servers by connecting an RDP (Remote Desktop Protocol) client application with an RDP server: https://en.wikipedia.org/wiki/Remote_Desktop_Protocol.
Allowing unrestricted RDP access can increase opportunities for malicious activity such as hacking, man-in-the-middle attacks (MITM) and Pass-the-Hash (PtH) attacks.
To determine if your EC2 security groups allow unrestricted RDP access, perform the following:
To update your security groups inbound/ingress configuration in order to restrict RDP access to specific entities (IP addresses, IP ranges, etc), perform the following: