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Description

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.

Rationale

Malicious activity, such as spoofing, brute-force, and FTP bounce attacks, can occur when permitting unfettered access to these ports.

Remediation

From the console

Follow the Security group rules docs to learn how to add a security group rule that will restrict access to a specific port.

From the command line

1. Run revoke-security-group-ingress to remove inbound rules that allow unrestricted access to port 20 and 21.

   revoke-security-group-egress.sh

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       aws ec2 revoke-security-group-egress
           --group-name your-group-name
           --protocol tcp
           --port 20
           --cidr 192.0.2.0/24
       

2. Run authorize-security-group-ingress to add new inbound rules that restrict FTP access.

   revoke-security-group-ingress.sh

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       aws ec2 authorize-security-group-ingress
           --group-name your-group-name
           --protocol tcp
           --port 20
           --cidr 192.0.2.0/24