nacl-outbound-restrict: Unrestricted NACL Outbound Traffic

id: nacl-outbound-restrict
info:
  name: Unrestricted NACL Outbound Traffic
  author: princechaddha
  severity: medium
  description: |
    Checks for Amazon VPC NACLs allowing outbound traffic to all ports, recommending restriction to necessary ports only.
  impact: |
    Potential for data exfiltration or unauthorized access if outbound traffic is not properly restricted.
  remediation: |
    Modify NACL outbound rules to limit traffic to only the ports required for legitimate business needs.
  reference:
    - https://docs.aws.amazon.com/vpc/latest/userguide/vpc-network-acls.html
  metadata:
    max-request: 2
  tags: cloud,devops,aws,amazon,vpc,aws-cloud-config
variables:
  region: "us-east-1"

flow: |
  code(1)
  for(let NACLIDs of iterate(template.nacls)){
    set("naclid", NACLIDs)
    code(2)
  }

self-contained: true
code:
  - engine:
      - sh
      - bash
    source: |
      aws ec2 describe-network-acls --region $region --query 'NetworkAcls[*].NetworkAclId' --output json

    extractors:
      - type: json
        name: nacls
        internal: true
        json:
          - '.[]'

  - engine:
      - sh
      - bash
    source: |
         aws ec2 describe-network-acls --region $region --network-acl-ids $naclid --query 'NetworkAcls[*].Entries[?(RuleAction==`allow`) && (Egress==`true`)] | []'

    matchers-condition: and
    matchers:
      - type: word
        words:
          - "allow"
        condition: and

      - type: word
        words:
          - "PortRange"
        negative: true

    extractors:
      - type: dsl
        dsl:
          - '"Access to the VPC subnets associated with your NACL " + naclid + " is not restricted."'
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