Ensure VPC peering routing tables have least access

Error: VPC peering routing tables do not have least access

Bridgecrew Policy ID: BC_AWS_NETWORKING_5
Severity: MEDIUM

VPC peering routing tables do not have least access

Description

Once a VPC peering connection is established, routing tables must be updated to establish any connections between the peered VPCs. These routes can be as specific as desired, even peering a VPC to only a single host on the other side of the connection.

Being highly selective in peering routing tables is a very effective way of minimizing the impact of a breach as resources outside of these routes are inaccessible to the peered VPC.

Fix - Runtime

Procedure

Remove and add route table entries to ensure that the least number of subnets or hosts required to accomplish the purpose for peering are routable.

CLI Command

To change the policy, use the following commands:

  1. For each route_table_id containing routes non-compliant with your routing policy (that grants more than desired least access), delete the non-compliant route:
aws ec2 delete-route 
--route-table-id <route_table_id> 
--destination-cidrblock  <non_compliant_destination_CIDR>
  1. Create a new compliant route:
aws ec2 create-route 
--route-table-id <route_table_id> 
--destination-cidrblock <compliant_destination_CIDR> 
--vpc-peering-connection-id <peering_connection_id>


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