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Silent Permission Enumeration via CloudTrail Logging Bypass on Non-Production Endpoints

Introduction

Cloud security is the cornerstone of modern infrastructure, and AWS has been at the forefront of ensuring robust security measures for its services. However, even the most secure platforms can have gaps that require attention. One such gap was identified in the Datazone service, where 44 non-production API endpoints were found to bypass CloudTrail logging. This bypass allowed adversaries to silently enumerate permissions using compromised AWS IAM credentials, undermining a critical detection capability.

This vulnerability highlights a subtle but significant risk: the ability to enumerate permissions on non-production endpoints without leaving a trace in CloudTrail logs. This article examines the vulnerability in depth, explains how it can be exploited, evaluates its impact, and provides recommendations for mitigation.

Understanding the Vulnerability

What is CloudTrail Logging?

AWS CloudTrail is a key service that provides governance, compliance, and operational and risk auditing for AWS accounts. It captures API calls and delivers logs to a designated S3 bucket or other destinations. These logs are invaluable for detecting unauthorized access attempts, including permission enumeration by compromised credentials.

Permission Enumeration and Its Importance

Permission enumeration is a reconnaissance technique where an attacker uses compromised AWS credentials to test which actions or resources they can access. This is typically achieved by making API calls and analyzing success or failure responses. For defenders, CloudTrail logs of such failed attempts serve as critical signals for detecting unauthorized activities.

The Core Issue

The vulnerability lies in the existence of non-production API endpoints for the AWS Datazone service that bypass CloudTrail logging. These endpoints accept standard IAM credentials and allow enumeration of permissions without generating logs in CloudTrail. This renders the activity invisible to security teams relying on CloudTrail for monitoring.

AWS has acknowledged this as a security concern, emphasizing that non-production endpoints callable with normal credentials and exhibiting IAM permission behavior should log to CloudTrail. Failure to do so creates a significant blind spot.

Exploitation Methodology

To understand the exploit, let’s consider the following scenario:

Setup: An adversary gains access to compromised AWS IAM credentials. These credentials are then used to enumerate permissions.
Observing the Normal Case: Using a standard production endpoint for the Datazone service, the adversary runs the following AWS CLI command:
```
aws datazone list-domains
```
This operation, even if it fails due to a lack of permissions, generates a CloudTrail log entry within 5-10 minutes. The entry provides defenders with visibility into the unauthorized attempt.
Exploiting the Non-Production Endpoints: The adversary switches to one of the non-production endpoints, such as:
```
aws datazone list-domains --endpoint-url https://jiaweid.gateway.us-east-1.test.api.niceland.aws.dev
```
After waiting the usual 5-10 minutes, they observe that no CloudTrail log is generated. Despite the absence of a log, the response of the API provides sufficient information to the adversary:
- If the request succeeds, the compromised identity has the required permissions.
- If the request fails with an AccessDeniedException, the identity lacks the required permissions.
Through this process, the adversary can systematically enumerate permissions without triggering any alerts.
Endpoints of Concern: The discovery revealed 44 non-production endpoints, including:
- jiaweid.gateway.us-east-1.test.api.niceland.aws.dev
- zhongwu.signin.us-east-1.test.api.niceland.aws.dev
- sobesim.gateway.us-east-1.test.api.niceland.aws.dev
These endpoints were likely intended for internal testing and development purposes but inadvertently introduced a significant security gap.

Impact Analysis

The implications of this vulnerability are noteworthy:

Silent Enumeration: Without CloudTrail logs, defenders have no visibility into enumeration activity. This allows attackers to stealthily map permissions, which is often the precursor to privilege escalation or lateral movement.
Compromised Detection Capabilities: Security teams relying on CloudTrail as their primary audit trail lose a critical signal, significantly delaying detection and response to unauthorized access.
Potential for Broader Exploitation: While these non-production endpoints did not grant access to customer data, the ability to enumerate permissions could enable attackers to pivot to other services or resources with higher privileges.
Reputational and Compliance Risks: The lack of visibility into unauthorized activities can lead to regulatory non-compliance and reputational damage for organizations leveraging AWS.

Mitigations and Preventive Measures

Addressing this vulnerability requires a combination of immediate fixes and long-term preventive measures:

Immediate Mitigations by AWS

AWS has already taken steps to resolve this issue:

The non-production endpoints were either updated to log to CloudTrail or taken offline.
Endpoint behavior was reviewed to ensure no further bypasses.

Recommendations for AWS Customers

Monitor Unusual Activity: Use AWS Config and GuardDuty to monitor for unusual API activity, especially on unusual endpoints.

Restrict Access to Non-Production Endpoints: Use IAM policies or VPC configurations to restrict access to non-production endpoints. For instance:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Action": "*",
      "Resource": "arn:aws:datazone:*:*:domain/*",
      "Condition": {
        "StringLike": {
          "aws:RequestURL": "*.test.api.niceland.aws.dev"
        }
      }
    }
  ]
}

Regular Audit of API Endpoints: Continuously verify that all API endpoints, including non-production ones, log to CloudTrail.
Least Privilege Principle: Limit permissions of IAM roles to only those required for their intended purpose.
Penetration Testing and Bug Bounty Programs: Encourage security researchers to identify similar issues through bug bounty programs or penetration testing efforts.

Recommendations for AWS

Mandatory CloudTrail Logging: Ensure that all API endpoints, including non-production ones, are configured to log to CloudTrail by default.
Internal Endpoint Review: Conduct regular reviews of all internal and non-production endpoints to identify and address potential gaps.
Endpoint Visibility for Customers: Provide customers with better visibility into endpoints exposed in their environments and their logging status.

Conclusion

The discovery of silent permission enumeration through non-production endpoints in the Datazone service is a stark reminder of the hidden risks in modern cloud environments. While the issue has been addressed, it underscores the importance of comprehensive logging and monitoring for all API endpoints.

By implementing the mitigations outlined above, AWS and its customers can strengthen their defenses against similar vulnerabilities. This case also highlights the critical role of security researchers in identifying and addressing gaps, ensuring that cloud platforms remain resilient against evolving threats.

The collaborative effort between the researcher and AWS demonstrates how transparency and swift action can resolve vulnerabilities effectively, ultimately making the cloud a safer place for all.