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Policy as Code: A Tale of Taming AWS Security Chaos

PUBLISHED:
May 29, 2025
|
BY:
Aneesh Bhargav
Ideal for
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Table of Contents

  1. The Wake-Up Call
  2. The Challenge: Managing Cloud Security at Scale
  3. Enter Policy as Code: The Game Changer
  4. Real-World Examples: From Chaos to Control
  5. The Implementation Journey
  6. The Results
  7. Getting Started with AppSecEngineer
  8. Additional Resources

‍

The Wake-Up Call

It was 3 AM when Sarah, a Senior Cloud Security Engineer at TechCorp, got the alert. Someone had accidentally exposed an S3 bucket containing sensitive customer data. As she scrambled to fix the issue, she thought, "There has to be a better way." This incident became the catalyst for TechCorp's journey into Policy as Code (PaC) - a journey that would transform their AWS security landscape forever.

‍

The Challenge: Managing Cloud Security at Scale

TechCorp's story isn't unique. With:

  • 500+ AWS accounts

  • 1000+ developers

  • 3000+ S3 buckets

  • Countless EC2 instances and Lambda functions

Manual security policy enforcement had become their biggest nightmare. Sound familiar?

‍

Enter Policy as Code: The Game Changer

What is Policy as Code?

Think of Policy as Code like a security guard who:

  • Never sleeps

  • Never makes mistakes

  • Works at lightning speed

  • Consistently enforces rules

  • Documents everything

But instead of a physical guard, it's all automated through code.

‍

Real-World Examples: From Chaos to Control

Example 1: The S3 Bucket Security Saga

The Problem

"

// Before: Vulnerable S3 Bucket Configuration
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": "*",
            "Action": "s3:GetObject",
            "Resource": "arn:aws:s3:::company-data/*"
        }
    ]
}

  
"

‍

The Solution: AWS Config Rule

"

# AWS Config Rule to enforce S3 encryption and block public access
def evaluate_compliance(configuration_item):
    s3_bucket = configuration_item['configuration']
    
    # Check for encryption
    if not s3_bucket.get('ServerSideEncryptionConfiguration'):
        return NON_COMPLIANT
        
    # Check for public access blocks
    if not s3_bucket.get('PublicAccessBlockConfiguration'):
        return NON_COMPLIANT
        
    public_access_block = s3_bucket['PublicAccessBlockConfiguration']
    if not all([
        public_access_block['BlockPublicAcls'],
        public_access_block['BlockPublicPolicy'],
        public_access_block['IgnorePublicAcls'],
        public_access_block['RestrictPublicBuckets']
    ]):
        return NON_COMPLIANT
    
    return COMPLIANT

  
"

‍

Example 2: The EC2 Instance Security Standard

The Problem

Developers were launching EC2 instances without proper security groups, tags, or encryption.

The Solution: CloudFormation Guard Rules

"

let ec2_instances = Resources.*[ Type == 'AWS::EC2::Instance' ]

# Rule 1: Ensure instances have required tags
rule ec2_required_tags when %ec2_instances !empty {
    %ec2_instances.Properties.Tags EXISTS
    %ec2_instances.Properties.Tags[*] {
        Key IN ['Environment', 'Owner', 'CostCenter', 'SecurityLevel']
    }
}

# Rule 2: Ensure instances use approved AMIs
rule ec2_approved_amis when %ec2_instances !empty {
    %ec2_instances.Properties.ImageId IN ['ami-approved1', 'ami-approved2']
}

# Rule 3: Ensure instances are encrypted
rule ec2_encryption when %ec2_instances !empty {
    %ec2_instances.Properties.BlockDeviceMappings[*].Ebs.Encrypted == true
}

  
"

‍

Example 3: The Lambda Function Security Framework

The Problem

Lambda functions with excessive permissions and no VPC configuration.

The Solution: Custom Terraform Validator

"

# Sentinel Policy for AWS Lambda
import "tfplan"

lambda_functions = filter tfplan.resource_changes as _, rc {
    rc.type is "aws_lambda_function" and
    (rc.change.actions contains "create" or rc.change.actions contains "update")
}

# Rule: Lambda must be in VPC
vpc_check = rule {
    all lambda_functions as _, function {
        keys(function.change.after.vpc_config) is not empty
    }
}

# Rule: Lambda role must follow least privilege
role_check = rule {
    all lambda_functions as _, function {
        function.change.after.role matches "arn:aws:iam::.*:role/lambda-restricted-.*"
    }
}

  
"

‍

The Implementation Journey

Phase 1: Foundation

  1. Tool Selection


    • AWS Config for continuous monitoring

    • CloudFormation Guard for IaC validation

    • Terraform with custom validators for infrastructure deployment

  2. Basic Policy Implementation

"

// Organization-wide SCP to prevent public S3 buckets
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "PreventPublicBuckets",
            "Effect": "Deny",
            "Action": [
                "s3:PutBucketPublicAccessBlock",
                "s3:DeletePublicAccessBlock"
            ],
            "Resource": "*",
            "Condition": {
                "StringEquals": {
                    "s3:PublicAccessBlockConfiguration": "false"
                }
            }
        }
    ]
}

  
"

‍

Phase 2: Automation

CI/CD Integration Example

"

# GitHub Actions workflow for policy validation
name: AWS Policy Validation
on: [pull_request]

jobs:
  validate:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Run CFN Guard
        run: |
          cfn-guard validate -r rules/* -d templates/*
      - name: Run Custom Validators
        run: |
          python3 validators/check_security_compliance.py
  
"


Phase 3: Monitoring and Enforcement (Week 5-6)

AWS EventBridge Rule for Real-time Monitoring

"

{
    "source": ["aws.config"],
    "detail-type": ["Config Rules Compliance Change"],
    "detail": {
        "configRuleName": ["s3-bucket-security-check"],
        "newEvaluationResult": {
            "complianceType": ["NON_COMPLIANT"]
        }
    }
}
  
"

‍

The Results

After implementing Policy as Code, TechCorp saw:

  • 99.9% reduction in security misconfigurations

  • 85% faster security policy updates

  • 100% audit compliance

  • Zero S3 bucket exposures

‍

Getting Started with AppSecEngineer

Ready to start your Policy as Code journey? AppSecEngineer offers:

  • Hands-on AWS security labs

  • Real-world policy implementation scenarios

  • Expert-guided learning paths  

‍

Additional Resources

Aneesh Bhargav

Blog Author
Aneesh Bhargav is the Head of Content Strategy at AppSecEngineer. He has experience in creating long-form written content, copywriting, producing Youtube videos and promotional content. Aneesh has experience working in Application Security industry both as a writer and a marketer, and has hosted booths at globally recognized conferences like Black Hat. He has also assisted the lead trainer at a sold-out DevSecOps training at Black Hat. An avid reader and learner, Aneesh spends much of his time learning not just about the security industry, but the global economy, which directly informs his content strategy at AppSecEngineer. When he's not creating AppSec-related content, he's probably playing video games.

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