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 25 in order to reduce the risk of common security threats for the SMTP server instances associated with your security groups. TCP port 25 is used by Simple Mail Transfer Protocol (SMTP) servers for email transmission.
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 inbound/ingress access on TCP port 25 (SMTP) to your Amazon EC2 instances can increase opportunities for malicious activities such as hacking, spamming, Shellshock, and Distributed Denial-of-Service (DDoS) attacks.
Audit
To determine if your Amazon EC2 security groups allow unrestricted SMTP access, perform the following operations:
Remediation / Resolution
To update the inbound rule configuration for your Amazon EC2 security groups in order to restrict Simple Mail Transfer Protocol (SMTP) 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
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You are auditing:
Unrestricted SMTP Access
Risk Level: Medium