Description

This policy identifies Google GCE Networks that have Firewall Rules allowing unrestricted incoming traffic (0.0.0.0/0) from the internet to NetBIOS ports: (TCP/UDP) 137, 138, and 139.

In GCP, Firewall Rules are defined at the VPC Network level. Each rule either allows or denies traffic based on its configuration. These configurations specify the type of traffic (e.g., protocols and ports) and the source or destination (e.g., IP addresses, subnets, and instances).

Rationale

NetBIOS is a legacy protocol used for name resolution and file/printer sharing in older Windows environments. It is not designed to be exposed to the public internet and has a long history of security vulnerabilities. Public exposure of these ports can lead to information disclosure, denial-of-service attacks, and exploitation by worms or malware that target NetBIOS services. There is almost no legitimate reason to allow unrestricted public access to these ports.

Impact

All NetBIOS connections from outside of the network to the concerned VPC(s) can be blocked. If there is a legitimate operational need for remote access, specific trusted source IP addresses should be explicitly defined in firewall rules to whitelist access only to the required NetBIOS ports.

Audit

This policy flags a Google GCE Network as INCOMPLIANT if it includes at least one Firewall Rule that meets all of the following conditions:

• Source Ranges is 0.0.0.0/0 or ::/0
• Direction is INGRESS
• Allowed Protocols / Ports JSON specifies the tcp or udp protocols and includes any of the following ports in the startPort - endPort range: 137, 138, 139.