Public ApplicationLoadBalancer with service 'NetBios Datagram Service' (TCP:138) 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: Application Load Balancer
CloudGuard Rule ID: D9.AWS.NET.AG2.7.ApplicationLoadBalancer.138.TCP
Covered by Spectral: No
Category: Networking & Content Delivery


ApplicationLoadBalancer where isPublic=true and inboundRules contain [port <= 138 and portTo >= 138 and protocol in ('TCP','ALL')] should not have inboundRules contain [port <= 138 and portTo >= 138 and protocol in ('TCP','ALL') and scope isPublic() and scope numberOfHosts() > 32 and scope numberOfHosts() <=  256]


Limit the access scope for ApplicationLoadBalancer with service 'NetBios Datagram 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.

Application Load Balancer

An Application Load Balancer functions at the application layer, the seventh layer of the Open Systems Interconnection (OSI) model. After the load balancer receives a request, it evaluates the listener rules in priority order to determine which rule to apply, and then selects a target from the target group for the rule action. You can configure listener rules to route requests to different target groups based on the content of the application traffic. Routing is performed independently for each target group, even when a target is registered with multiple target groups.

Compliance Frameworks

  • BP-0318
  • LGPD