Hijacking the Cloud: An AWS Takeover and RCE Tale at XYZ Company

In today’s fast-paced cloud era, even seasoned engineers can overlook subtle misconfigurations that open the door to catastrophic breaches. In this deep-dive, we’ll follow a hypothetical—but entirely plausible—attack chain against XYZ Company, a mid-sized e-commerce startup running key services on AWS. Through a blend of Server-Side Request Forgery (SSRF), AWS metadata abuse, and Remote Code Execution (RCE), attackers achieve full AWS takeover—and then we’ll explore how the defenders could have stopped them.

Background: XYZ Company’s Cloud Stack

• Public-facing API Gateway routing to Lambda functions for product images

• Amazon S3 buckets hosting static assets (images, CSS, JS)

• Amazon ECS clusters running containerized microservices (Node.js, Python)

• RDS MySQL for transactional data, with a bastion EC2 only allowing SSH from corporate IPs

• AWS Identity and Access Management (IAM) with scoped roles but a handful of overly broad policies

On paper, XYZ follows many AWS best practices—separation of environments, least privilege roles, CloudTrail logging. Yet a single SSRF bug in an image-processing Lambda unlocked the keys to the kingdom.

Phase 1: Hijacking the Cloud via Reconnaissance & Vulnerability Discovery

1. Fuzzing the Image API The attacker discovers a feature in the GET /api/v1/images?url= endpoint. When you pass a URL, the Lambda fetches that address, processes the image, and returns a thumbnail.

2. Testing for SSRF By supplying http://169.254.169.254/latest/meta-data/iam/security-credentials/ as the url parameter, the attacker bypasses input sanitization. The Lambda dutifully queries the AWS Instance Metadata Service (IMDS) at 169.254.169.254 and returns the IAM role name attached to the execution environment.

Tech Spotlight

• IMDS (Instance Metadata Service): A special HTTP endpoint available to EC2 instances and certain AWS-managed runtimes, exposing temporary credentials and metadata.

• SSRF (Server-Side Request Forgery): When an attacker coerces the server to make HTTP requests on their behalf, often to internal or privileged endpoints.

Phase 2: Hijacking the Cloud via Credential Harvesting & Privilege Escalation

1. Retrieving STS Tokens Next, the attacker passes http://169.254.169.254/latest/meta-data/iam/security-credentials/<RoleName>. The Lambda returns temporary AWS credentials (AccessKeyId, SecretAccessKey, SessionToken) with whatever permissions the role grants.

2. Assessing Permissions The compromised Lambda role has iam:ListUsers and sts:AssumeRole on a development account role. By chaining sts:AssumeRole, the attacker elevates privileges to an admin role in dev, then pivots back to the prod account via a trust policy.

Tech Spotlight

• STS AssumeRole: Lets one AWS principal take on another role’s permissions, given the right trust relationship.

• IAM Policy Scope: Even a single ‘overly broad’ statement (e.g., Resource: *) can be fatal.

Phase 3: Hijacking the Cloud via Spinning Up Malicious Infrastructure

With admin-level credentials in hand, the adversary can:

1. Create a Backdoor EC2

   • Launch an EC2 instance in a quiet VPC with a public IP

   • Assign it an IAM role granting full access to S3, RDS, Lambda, CloudFormation

2. Inject Rogue Lambda Function

   • Deploy a new Lambda that, on invocation, RCEs inside other functions by patching their environment variables or updating their code via the AWS SDK.

3. Establish Persistence

   • Update the AWS Organization’s SCPs to whitelist attacker accounts

   • Enable CloudWatch Events to trigger the rogue Lambda on every S3 PutObject

   
   

Phase 4: Hijacking via Remote Code Execution (RCE)

The crux of the takeover is RCE in existing services:

1. Lambda Code InjectionUsing the admin API, the attacker calls UpdateFunctionCode on key functions—embedding a reflective shell that exfiltrates credentials on every invocation.

2. Container Compromise in ECSWith ECS service definitions editable, they inject a sidecar container that runs a reverse shell. This container mounts the same IAM role via the ECS task role.

3. Cross-Service PivotingFrom ECS, they connect to the RDS bastion host (since the ECS SGs allow traffic to the bastion), harvesting full database dumps of customer PII.

Real-World Impact on XYZ Company

• Data Exfiltration: Millions of customer records, including payment tokens.

• Service Disruption: Malicious CloudFormation stacks delete production resources at odd hours.

• Compliance Breach: Violation of GDPR/CCPA leading to fines and reputational damage.

• Financial Hit: Weeks of downtime, forensic investigations, and regulatory penalties.

Lessons Learned & Mitigations

1. Enforce IMDSv2 Require AWS SDK clients to negotiate session tokens (via PUT X-aws-ec2-metadata-token-ttl-seconds)—blocking SSRF-based metadata pulls.

2. Tighten IAM Policies

   • Avoid Resource: "*".

   • Use permission boundaries and session policies to constrain assumed roles.

3. Harden Public APIs

   • Sanitize and whitelist external URLs.

   • Implement URL fetch limiting or proxy through vetted endpoints only.

4. Network Segmentation

   • Isolate sensitive services (e.g., RDS, bastion) in private subnets with strict SGs.

   • Block egress to 169.254.169.254 wherever possible.

5. Continuous Monitoring

   • Enable GuardDuty for anomalous STS calls.

   • Alert on new role creations, CloudFormation stack updates, and unexpected Lambda code changes.

Conclusion

Cloud platforms like AWS offer remarkable agility—but with that power comes the need for relentless vigilance. As our XYZ Company saga shows, a tiny SSRF flaw can escalate into a full-blown AWS takeover with devastating RCE capabilities. By adopting IMDSv2, practicing least-privilege IAM, and continuously monitoring for anomalous API calls, you can fortify your cloud perimeter against these real-world threats. Stay proactive, stay secure!