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 139 and UDP ports 137 and 138 in order to reduce the possibility of a security breach and protect the EC2 instances associated with your security groups. TCP port 139 and UDP ports 137 and 138 are used for NetBIOS name resolution (i.e. mapping a NetBIOS name to an IP address) by services such as File and Printer Sharing service running on Microsoft Windows Server OS.
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 NetBIOS access to your Amazon EC2 instances can increase opportunities for malicious activities such as man-in-the-middle attacks (MITM), Denial of Service (DoS) attacks or BadTunnel exploits.
Audit
To determine if your Amazon EC2 security groups allow unrestricted NetBIOS access, perform the following actions:
Remediation / Resolution
To update the inbound rule configuration for your Amazon EC2 security groups in order to restrict NetBIOS access to trusted entities only (i.e. authorized IP addresses and IP ranges, or other security groups), perform the following actions:
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 NetBIOS Access
Risk Level: Medium