implementing-gcp-vpc-firewall-rules

name	implementing-gcp-vpc-firewall-rules
description	Implements and audits GCP VPC firewall rules using gcloud, covering auditing overly permissive rules, creating restrictive ingress/egress rules, hierarchical firewall policies, and monitoring rule effectiveness with VPC Flow Logs. Use when deploying GCP workloads needing network access controls, auditing firewall configs, or responding to Security Command Center findings; not for Cloud Armor or DNS-based filtering.
domain	cybersecurity
subdomain	cloud-security
tags	["cloud-security","gcp","vpc","firewall-rules","network-security","segmentation"]
version	1.0
author	mahipal
license	Apache-2.0
nist_csf	["PR.IR-01","ID.AM-08","GV.SC-06","DE.CM-01"]
mitre_attack	["T1078.004","T1530","T1537","T1580"]

Implementing GCP VPC Firewall Rules

When to Use

• When deploying new GCP workloads that require network-level access controls
• When auditing existing firewall configurations for overly permissive rules
• When implementing zero trust network segmentation within GCP VPC networks
• When responding to Security Command Center findings about open firewall rules
• When building hierarchical firewall policies across a GCP organization

Do not use for application-layer filtering (use Cloud Armor WAF), for DNS-based filtering (use Cloud DNS response policies), or for VPN/interconnect traffic filtering without understanding that VPC firewall rules apply to traffic within the VPC.

Prerequisites

• GCP project with Compute Engine API enabled
• IAM roles: roles/compute.securityAdmin for firewall management, roles/compute.networkViewer for auditing
• Organization Admin role for hierarchical firewall policies
• gcloud CLI authenticated with appropriate permissions
• VPC Flow Logs enabled on target subnets for monitoring

Workflow

Step 1: Audit Existing Firewall Rules for Security Gaps

Enumerate all firewall rules and identify overly permissive configurations.

# List all firewall rules in the project
gcloud compute firewall-rules list \
  --format="table(name, network, direction, priority, allowed[].map().firewall_rule().list():label=ALLOWED, sourceRanges, targetTags)"

# Find rules allowing all traffic from 0.0.0.0/0
gcloud compute firewall-rules list \
  --filter="direction=INGRESS AND sourceRanges=0.0.0.0/0" \
  --format="table(name, network, allowed, priority, targetTags)" \
  --sort-by=priority

# Find rules allowing all protocols and ports
gcloud compute firewall-rules list \
  --filter="direction=INGRESS AND allowed[].IPProtocol=all" \
  --format="table(name, network, sourceRanges, targetTags)"

# Find rules with SSH (22) or RDP (3389) open to the internet
gcloud compute firewall-rules list \
  --filter="direction=INGRESS AND sourceRanges=0.0.0.0/0 AND (allowed[].ports=22 OR allowed[].ports=3389)" \
  --format="table(name, network, allowed, sourceRanges)"

# Check for disabled rules
gcloud compute firewall-rules list \
  --filter= \
  --format=