Check for Unrestricted Outbound Access on All Ports

ID: gcloud-unrestricted-outbound-access

Severity: high

Author: princechaddha

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

Description

Check your Google Cloud VPC network firewall for any egress rules that allow unrestricted access (0.0.0.0/0) to any TCP/UDP ports. Restrict outbound traffic to only those IP addresses and/or IP ranges that require it in order to implement the principle of least privilege and reduce the attack surface.

YAML Source

id: gcloud-unrestricted-outbound-access

info:
  name: Check for Unrestricted Outbound Access on All Ports
  author: princechaddha
  severity: high
  description: |
    Check your Google Cloud VPC network firewall for any egress rules that allow unrestricted access (0.0.0.0/0) to any TCP/UDP ports. Restrict outbound traffic to only those IP addresses and/or IP ranges that require it in order to implement the principle of least privilege and reduce the attack surface.
  impact: |
    Allowing unrestricted outbound access on all ports increases the risk of data exfiltration and potential exploitation of cloud resources.
  remediation: |
    Update your VPC firewall rules to restrict outbound traffic to trusted IP addresses and ports only.
  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,destinationRanges,allowed[].ports)"

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

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

      let insecureRules = [];
      for (let rule of firewallRules) {
        if (
          rule.disabled === false &&
          rule.direction === "EGRESS" &&
          Array.isArray(rule.destinationRanges) && rule.destinationRanges.includes("0.0.0.0/0") &&
          Array.isArray(rule.allowed) &&
          rule.allowed.some(allowed =>
            Array.isArray(allowed.ports) &&
            (allowed.ports.includes("0-65535") || allowed.ports.some(port => port.startsWith("tcp:0-") || port.startsWith("udp:0-")))
          )
        ) {
          insecureRules.push(rule.name);
        }
      }

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

    extractors:
      - type: dsl
        dsl:
          - response
# digest: 4a0a0047304502205b6b56ab0cfddd7d7dd5709871ffbd78482b86a25fc097fab7999d4f5e4556050221009c663a2a02fe85a229371fe8c536dd5157538a5cfc5ea7c86541db7108c13625:922c64590222798bb761d5b6d8e72950

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-outbound-access.yaml"

View on Github