NetworkLoadBalancer with service 'SMTP' (TCP:25) is exposed to a wide network scope

Risk Level: Medium
Cloud Entity: Network Load Balancer
CloudGuard Rule ID: D9.AWS.NET.AG2.6.NetworkLoadBalancer.25.TCP
Covered by Spectral: No
Category: Networking & Content Delivery

GSL LOGIC

NetworkLoadBalancer where inboundRules contain [port <= 25 and portTo >= 25 and protocol in ('TCP','ALL')] should not have inboundRules contain [port <= 25 and portTo >= 25 and protocol in ('TCP','ALL') and scope numberOfHosts() > 256]

REMEDIATION

Limit the access scope for NetworkLoadBalancer with service 'SMTP 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: http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/authorizing-access-to-an-instance.html

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 https://sc1.checkpoint.com/documents/CloudGuard_Dome9/Documentation/Network-Security/FullProtectionMode.html?Highlight=full%20protection 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
• NETWSEC-V2