Public Instance with service 'NetBios Session Service' (TCP:139) is exposed to a small public network

Services and databases store data that may be sensitive, protected by law, subject to regulatory requirements or compliance standards. It is highly recommended that access to data will be restricted to encrypted protocols. This rule detects network settings that may expose data via unencrypted protocol over the public internet or to a too wide local scope.

Risk Level: Medium
Cloud Entity: Amazon EC2 Instance
CloudGuard Rule ID: D9.AWS.NET.AG2.7.Instance.139.TCP
Covered by Spectral: No
Category: Compute


Instance where isPublic=true and inboundRules contain [port <= 139 and portTo >= 139 and protocol in ('TCP','ALL')] should not have inboundRules contain [port <= 139 and portTo >= 139 and protocol in ('TCP','ALL') and scope isPublic() and scope numberOfHosts() > 32 and scope numberOfHosts() <=  256]


Limit the access scope for Instance with service 'NetBios Session Service to only allow access in internal networks and limited scope.

If public interface exists, remove it and limit the access scope within the VPC only to applications or instances that requires access.

Amazon Reference:

As a further protection step, Use CloudGuard 'Tamper Protection' (Full Protection mode) and region lock to prevent unauthorized changes to network access settings, refer to for more details.

Refer to for more details.

Amazon EC2 Instance

Amazon Elastic Compute Cloud (Amazon EC2) is a web service that provides secure, resizable compute capacity in the cloud. It is designed to make web-scale cloud computing easier for developers.

Compliance Frameworks

  • BP-0318
  • LGPD