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Version: 4.2.0

How to Find AWS EC2 Security Groups Allowing All Inbound Traffic on Default Telnet Ports

If security groups are not properly configured, the attack surface is increased.

info

This security check is part of the CIS Amazon Web Services Benchmarks and is rated severity high.

Prerequisites​

This guide assumes that you have already installed and configured Fix Inventory to collect your AWS resources.

Directions​

  1. Execute the following search command in Fix Inventory Shell:

    > search is(aws_ec2_security_group) and group_ip_permissions[*].{(ip_protocol=-1 or (from_port>=23 and to_port<=23 and ip_protocol=tcp)) and (ip_ranges[*].cidr_ip="0.0.0.0/0" or ipv6_ranges[*].cidr_ipv6="::/0")}
    ​kind=aws_ec2_security_group, ..., region=fixinventory-poweruser
    ​kind=aws_ec2_security_group, ..., account=poweruser-team

  2. Pipe the search command into the dump command:

    > search is(aws_ec2_security_group) and group_ip_permissions[*].{(ip_protocol=-1 or (from_port>=23 and to_port<=23 and ip_protocol=tcp)) and (ip_ranges[*].cidr_ip="0.0.0.0/0" or ipv6_ranges[*].cidr_ipv6="::/0")} | dump
    ​reported:
    ​  id: /aws/ec2/123
    ​  name: some-name
    ​  ctime: '2022-12-05T22:53:14Z'
    ​  kind: aws_ec2_security_group
    ​  age: 2mo28d

    The command output will list the details of all non-compliant aws_ec2_security_group resources.

Remediation​

  • Apply Zero Trust approach.
  • Implement a process to scan and remediate unrestricted or overly permissive network ACLs.
  • Recommended best practices is to narrow the definition for the minimum ports required.
note

Please refer to the AWS EC2 documentation for details.

Further Reading​