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Description

The Network Access Control List (NACL) function provide stateless filtering of ingress and egress network traffic to AWS resources. It is recommended that no NACL allows unrestricted ingress access to remote server administration ports, such as SSH to port 22 and RDP to port 3389, using either the TCP (6), UDP (17) or ALL (-1) protocol.

Rationale​

Public access to remote server administration ports, such as 22 and 3389, increases resource attack surface and unnecessarily raises the risk of resource compromise.

Audit​

From Console​

Perform the following to determine if the account is configured as prescribed:

  1. Login to the AWS Management Console at https://console.aws.amazon.com/vpc/home.

  2. In the left pane, click Network ACLs.

  3. For each network ACL, perform the following:

    • Select the network ACL.
    • Click the Inbound Rules tab.
    • Ensure no rule exists that has a port range that includes port 22, 3389, using the protocols TCP (6), UDP (17) or ALL (-1) or other remote server administration ports for your environment and has a Source of 0.0.0.0/0 and shows ALLOW.

Note: A Port value of ALL or a port range such as 0-1024 are inclusive of port 22, 3389, and other remote server administration ports.

References​

  1. https://docs.aws.amazon.com/vpc/latest/userguide/vpc-network-acls.html
  2. https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Security.html#VPC_Security_Comparison