​Understanding the Security Risks of ECS Instance Metadata and STS Credentials​

 

Introduction

Amazon Elastic Compute Service (ECS) provides scalable computing capacity in the cloud, allowing developers to run applications without managing servers. However, with this convenience comes the responsibility of ensuring the security of ECS instances. One significant security concern involves the potential exploitation of the instance metadata service to obtain temporary security credentials, leading to unauthorized access and lateral movement within the cloud environment.​

The Role of Instance Metadata and STS Credentials

Each ECS instance has access to an instance metadata service, which provides information about the instance, including temporary security credentials associated with the instance's IAM role. These credentials are obtained via the AWS Security Token Service (STS) and are used by applications running on the instance to access AWS resources securely.​

Exploitation via Server-Side Request Forgery (SSRF)

A common attack vector involves exploiting Server-Side Request Forgery (SSRF) vulnerabilities in applications running on ECS instances. An attacker can manipulate the application to send requests to the instance metadata service's endpoint (http://169.254.169.254), retrieving the temporary STS credentials. With these credentials, the attacker can gain unauthorized access to AWS resources, potentially leading to data breaches or further compromise of the cloud environment.​

Real-World Implications

The Capital One data breach in 2019 is a notable example of such an attack. An attacker exploited an SSRF vulnerability to access the instance metadata service, obtaining STS credentials and compromising sensitive customer data. This incident underscores the critical need for securing access to instance metadata.​

Mitigation Strategies

To protect against such vulnerabilities:

1. Enforce the use of Instance Metadata Service Version 2 (IMDSv2): IMDSv2 requires session-based tokens, adding an extra layer of security against unauthorized access.​

2. Implement strict input validation: Ensure that applications validate and sanitize user inputs to prevent SSRF vulnerabilities.​

3. Restrict IAM role permissions: Follow the principle of least privilege, granting only necessary permissions to IAM roles associated with ECS instances.​

4. Monitor and log access to metadata endpoints: Use monitoring tools to detect unusual access patterns to the instance metadata service.​

Recommended Product

To enhance the security of your ECS instances, consider using the AWS Systems Manager Session Manager. This service allows secure and auditable instance management without the need to open inbound ports, maintain bastion hosts, or manage SSH keys.​

Conclusion

Securing ECS instances against metadata service exploitation is crucial for maintaining the integrity of your cloud environment. By understanding the risks and implementing robust security measures, organizations can protect their resources from unauthorized access and potential breaches.​