Check for Unrestricted Inbound Access on Uncommon Ports

ID: gcloud-unrestricted-inbound-uncommon-ports

Severity: high

Author: princechaddha

Tags: cloud,devops,gcp,gcloud,vpc,firewall,security,networking,gcp-cloud-config

Description

Ensure that your Virtual Private Cloud (VPC) firewall rules do not allow unrestricted access (0.0.0.0/0) to any uncommon ports to protect against brute force attacks targeting virtual machine instances associated with these firewall rules. Uncommon ports are TCP/UDP ports not included in the common service ports category.

YAML Source

id: gcloud-unrestricted-inbound-uncommon-ports

info:
  name: Check for Unrestricted Inbound Access on Uncommon Ports
  author: princechaddha
  severity: high
  description: |
    Ensure that your Virtual Private Cloud (VPC) firewall rules do not allow unrestricted access (0.0.0.0/0) to any uncommon ports to protect against brute force attacks targeting virtual machine instances associated with these firewall rules. Uncommon ports are TCP/UDP ports not included in the common service ports category.
  impact: |
    Allowing unrestricted access to uncommon ports increases the attack surface and exposes cloud resources to potential brute-force or unauthorized access attacks.
  remediation: |
    Update your VPC firewall rules to allow traffic only to common ports required for your applications, and restrict access to uncommon ports.
  reference:
    - https://cloud.google.com/vpc/docs/firewalls
  tags: cloud,devops,gcp,gcloud,vpc,firewall,security,networking,gcp-cloud-config

flow: |
  code(1)
  for(let projectId of iterate(template.projectIds)){
    set("projectId", projectId)
    code(2)
    for(let networkName of iterate(template.networks)){
      set("networkName", networkName)
      code(3)
      set("firewallRules", template.firewallRules)
      javascript(1)
    }
  }

self-contained: true

code:
  - engine:
      - sh
      - bash
    source: |
      gcloud projects list --format="json(projectId)"

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

  - engine:
      - sh
      - bash
    source: |
      gcloud compute networks list --project $projectId --format="json(name)"

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

  - engine:
      - sh
      - bash
    source: |
      gcloud compute firewall-rules list --filter network=$networkName --sort-by priority --format="json(name,disabled,direction,sourceRanges,allowed[].ports)"

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

javascript:
  - code: |
      let firewallRules = template.firewallRules;
      if (typeof firewallRules === "string") {
        firewallRules = JSON.parse(firewallRules);
      }

      const commonPorts = [
        "80", "443", "20", "21", "22", "23", "53", "3389",
        "25", "465", "587", "3306", "5432", "1521", "1433",
        "135", "137", "138", "139", "445"
      ];

      let insecureRules = [];
      for (let rule of firewallRules) {
        if (
          rule.disabled === false &&
          rule.direction === "INGRESS" &&
          Array.isArray(rule.sourceRanges) && rule.sourceRanges.includes("0.0.0.0/0") &&
          Array.isArray(rule.allowed) &&
          rule.allowed.some(allowed =>
            Array.isArray(allowed.ports) &&
            allowed.ports.some(port => !commonPorts.includes(port))
          )
        ) {
          insecureRules.push(rule.name);
        }
      }

      if (insecureRules.length > 0) {
        Export(`The firewall rules in network ${template.networkName} of project ${template.projectId} allow unrestricted access on uncommon ports: ${insecureRules.join(", ")}`);
      }

    extractors:
      - type: dsl
        dsl:
          - response
# digest: 4b0a00483046022100ca3e9ccc5b79485a6429f83e8593cdad7d0434d2f735dc8b4af657cb4bb14caf022100fceee091970ffed5f6e54d40927e6a6b90f330cdaee58908ca27bb979bbac155:922c64590222798bb761d5b6d8e72950

Guide to check the vulnerabilities

This template is used to detect vulnerabilities in web applications. It can be used with the Nuclei tool to scan for specific patterns or behaviors.

$ nuclei -u "URL" -t "cloud/gcp/vpc/gcloud-unrestricted-inbound-uncommon-ports.yaml"

View on Github