Public NetworkLoadBalancer with service 'NetBios Session Service' (TCP:139) is exposed to the entire internet

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: High
Cloud Entity: Network Load Balancer
CloudGuard Rule ID: D9.AWS.NET.AG2.8.NetworkLoadBalancer.139.TCP
Covered by Spectral: No
Category: Networking & Content Delivery


NetworkLoadBalancer where isPublic=true and nics contain [ subnet.routeTable.associations length()>0 ] and nics contain [ subnet.routeTable.routes contain [ destinationCidrBlock='' and gatewayId regexMatch /gw/ ] ] should not have inboundRules contain [ port<=139  and portTo>=139  and protocol in ('TCP', 'ALL') and scope isPublic() and scope='']


Limit the access scope for NetworkLoadBalancer 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.

Network Load Balancer

A Network Load Balancer functions at the fourth layer of the Open Systems Interconnection (OSI) model. It can handle millions of requests per second. After the load balancer receives a connection request, it selects a target from the target group for the default rule. It attempts to open a TCP connection to the selected target on the port specified in the listener configuration.

Compliance Frameworks

  • BP-0318
  • LGPD