Check your Amazon EC2 security groups for inbound rules that allow unrestricted access (i.e. 0.0.0.0/0 or ::/0) on TCP port 23 in order to reduce the exposure to security risks and protect the EC2 instances associated with your security groups. TCP port 23 is used by the Telnet server application (telnetd). Telnet is usually used to check whether a client can make TCP/IP connections to a particular service.
This rule can help you with the following compliance standards:
- PCI
- APRA
- MAS
- NIST4
For further details on compliance standards supported by Conformity, see here.
This rule can help you work with the AWS Well-Architected Framework.
This rule resolution is part of the Conformity Security & Compliance tool for AWS.
Allowing unrestricted ingress/inbound access on TCP port 23 (Telnet) through Amazon EC2 security groups can increase opportunities for malicious activities such as IP address spoofing, man-in-the-middle attacks (MITM) and brute-force attacks.
Audit
To determine if your Amazon EC2 security groups allow unrestricted Telnet access, perform the following operations:
Remediation / Resolution
To update the inbound rule configuration for your Amazon EC2 security groups in order to restrict Telnet-based access to trusted entities only (i.e. authorized IP addresses and IP ranges, or other security groups), perform the following operations:
References
- AWS Documentation
- Amazon EC2 security groups for Linux instances
- Work with security groups
- Security group rules for different use cases
- Authorize inbound traffic for your Linux instances
- AWS Command Line Interface (CLI) Documentation
- ec2
- describe-security-groups
- revoke-security-group-ingress
- authorize-security-group-ingress