Reduce the probability of a breach by checking EC2 security groups for inbound rules that allow unfettered access to TCP ports 20 and 21 (used by client/server applications for communication and file transfer) and restrict access to IP addresses that require this port.
Malicious activity, such as spoofing, brute-force, and FTP bounce attacks, can occur when permitting unfettered access to these ports.
Follow the Security group rules docs to learn how to add a security group rule that will restrict access to a specific port.
revoke-security-group-ingress to remove inbound rules that allow unrestricted access to port 20 and 21.
aws ec2 revoke-security-group-egress --group-name your-group-name --protocol tcp --port 20 --cidr 192.0.2.0/24
authorize-security-group-ingress to add new inbound rules that restrict FTP access.
aws ec2 authorize-security-group-ingress --group-name your-group-name --protocol tcp --port 20 --cidr 192.0.2.0/24