/auditing-terraform-infrastructure-for-security

name: auditing-terraform-infrastructure-for-security
description: 'Auditing Terraform infrastructure-as-code for security misconfigurations
  using Checkov, tfsec, Terrascan, and OPA/Rego policies to detect overly permissive
  IAM policies, public resource exposure, missing encryption, and insecure defaults
  before cloud deployment.

  '
domain: cybersecurity
subdomain: cloud-security
tags:
- cloud-security
- terraform
- infrastructure-as-code
- checkov
- tfsec
- policy-as-code
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
- T1190
- T1552.001
- T1580

Auditing Terraform Infrastructure for Security

When to Use

• When integrating security scanning into CI/CD pipelines for Terraform deployments
• When reviewing Terraform plans and modules for security best practices before applying
• When building policy-as-code guardrails for cloud infrastructure provisioning
• When auditing existing Terraform state files to identify deployed misconfigurations
• When enforcing organizational security standards across multiple Terraform projects

**Do not use** for runtime security monitoring (use CSPM tools), for application security testing (use SAST/DAST tools), or for cloud configuration drift detection (use AWS Config or Azure Policy after deployment).

Prerequisites

• Checkov installed (`pip install checkov`)
• tfsec installed (`brew install tfsec` or binary from GitHub)
• Terrascan installed (`brew install terrascan`)
• Terraform v1.0+ for plan generation
• OPA (Open Policy Agent) for custom policy enforcement
• Git repository with Terraform code to audit

Workflow

Step 1: Scan Terraform Code with Checkov

Run Checkov for comprehensive IaC security scanning with built-in and custom policies.

# Scan a Terraform directory
checkov -d ./terraform/ --framework terraform

# Scan with specific check categories
checkov -d ./terraform/ --check CKV_AWS_18,CKV_AWS_19,CKV_AWS_20,CKV_AWS_21

# Scan and output results in JSON
checkov -d ./terraform/ --output json > checkov-results.json

# Scan a Terraform plan file for more accurate analysis
terraform init && terraform plan -out=tfplan
terraform show -json tfplan > tfplan.json
checkov -f tfplan.json --framework terraform_plan

# Skip specific checks with justification
checkov -d ./terraform/ --skip-check CKV_AWS_145 \
  --bc-api-key $BRIDGECREW_API_KEY

# Scan Terraform modules
checkov -d ./modules/ --framework terraform --compact

# List all available checks
checkov --list --framework terraform | grep CKV_AWS

Step 2: Scan with tfsec for Terraform-Specific Issues

Use tfsec for Terraform-native security analysis with detailed remediation guidance.

# Scan a Terraform directory
tfsec ./terraform/

# Scan with minimum severity threshold
tfsec ./terraform/ --minimum-severity HIGH

# Output in JSON for CI/CD processing
tfsec ./terraform/ --format json > tfsec-results.json

# Scan with custom checks
tfsec ./terraform/ --custom-check-dir ./custom-checks/

# Exclude specific rules
tfsec ./terraform/ --exclude-downloaded-modules \
  --exclude aws-s3-enable-bucket-logging

# Scan and fail on specific severity
tfsec ./terraform/ --minimum-severity CRITICAL --soft-fail

# Generate SARIF output for GitHub Security tab
tfsec ./terraform/ --format sarif > tfsec.sarif

Step 3: Run Terrascan for Multi-Framework Compliance

Execute Terrascan for compliance checking against CIS, NIST, and SOC 2 frameworks.

# Scan Terraform against CIS AWS benchmark
terrascan scan -t aws -i terraform -d ./terraform/ \
  --policy-type aws --verbose

# Scan against specific compliance frameworks
terrascan scan -t aws -i terraform -d ./terraform/ \
  --policy-type aws \
  --categories "Compliance Validation"

# Output in JSON
terrascan scan -t aws -i terraform -d ./terraform/ \
  --output json > terrascan-results.json

# Scan a Terraform plan
terrascan scan -t aws -i terraform \
  --iac-file tfplan.json \
  --iac-type tfplan

# List available policies
terrascan scan --list-policies -t aws

Step 4: Create Custom OPA Policies for Organization Standards

Write Rego policies for organization-specific security requirements.

# policy/aws_s3_encryption.rego
package terraform.aws.s3

deny[msg] {
    resource := input.resource.aws_s3_bucket[name]
    not resource.server_side_encryption_configuration
    msg := sprintf("S3 bucket '%s' must have server-side encryption enabled", [name])
}

# policy/aws_iam_no_wildcards.rego
package terraform.aws.iam

deny[msg] {
    resource := input.resource.aws_iam_policy[name]
    statement := resource.policy.Statement[_]
    statement.Action == "*"
    statement.Effect == "Allow"
    msg := sprintf("IAM policy '%s' must not use wildcard (*) actions", [name])
}

deny[msg] {
    resource := input.resource.aws_iam_policy[name]
    statement := resource.policy.Statement[_]
    statement.Resource == "*"
    statement.Effect == "Allow"
    contains(statement.Action[_], "*")
    msg := sprintf("IAM policy '%s' has overly permissive actions on wildcard resources", [name])
}

# policy/aws_no_public_ingress.rego
package terraform.aws.security_group

deny[msg] {
    resource := input.resource.aws_security_group_rule[name]
    resource.type == "ingress"
    resource.cidr_blocks[_] == "0.0.0.0/0"
    resource.from_port <= 22
    resource.to_port >= 22
    msg := sprintf("Security group rule '%s' allows SSH from 0.0.0.0/0", [name])
}

# Evaluate Terraform plan against OPA policies
terraform show -json tfplan | opa eval \
  --data ./policy/ \
  --input /dev/stdin \
  "data.terraform.aws" \
  --format pretty

# Run Conftest for easier OPA policy testing
conftest test tfplan.json --policy ./policy/ --output json

Step 5: Integrate Security Scanning into CI/CD Pipeline

Add IaC security scanning as a mandatory CI/CD gate.

# GitHub Actions: Terraform security pipeline
name: Terraform Secur