Detailed Technical Analysis of "Cloning Internal Google Repos for Fun and Info"

Overview:
Luke Berner's write-up provides insight into how he exploited a misconfiguration in Google Cloud Source Repositories to clone internal Google repositories. This analysis dissects the technical aspects of his findings and methodologies used to achieve this.

Key Technical Details:

  1. Google Cloud Source Repositories (GCSR):
    GCSR allows Google Cloud users to host Git repositories. These repositories can be configured with fine-grained access controls to restrict who can view and modify the content.

  2. Misconfiguration Exploitation:

  3. Repository Access Controls: The critical misconfiguration lay in the repository access controls. Berner found that some repositories, which were meant to be private, were misconfigured to be publicly accessible.

  4. IAM Policies: Google Cloud’s Identity and Access Management (IAM) system governs access. Inappropriately set IAM policies led to wider access than intended. Specifically, read permissions granted to "allAuthenticatedUsers" or "allUsers" make repositories publicly accessible to those who either have a Google account or even anonymous users, respectively.

  5. Identifying Vulnerable Repositories:

  6. Google Dorking: Berner used Google search operators to locate potentially vulnerable repositories. By searching for specific terms and patterns indicative of Google Cloud Source Repository URLs, he could identify publicly exposed repositories.

  7. Enumerating Repositories: He constructed URLs based on common naming conventions and project structures to find repositories that might be publicly accessible.

  8. Cloning Repositories:

  9. Repo Listings: After identifying potential target repositories, Berner attempted to access them using Git commands. The simplicity of git clone allowed him to pull down entire repositories if they were misconfigured to be public.

  10. Access Validation: Direct access attempts often revealed informative error messages, which helped in enumerating and validating access levels.

  11. Identifying Sensitive Information:

  12. Repository Contents: Once repositories were cloned, they revealed sensitive information like source code, API keys, credentials, internal documentation, and project configurations.

  13. Security Impact: The exposed information could potentially lead to severe security implications, such as further exploitation, privilege escalation within the Google environment, or intellectual property theft.

  14. Disclosure and Remediation:

  15. Responsible Disclosure: Berner responsibly reported the issue to Google, allowing them to correct the misconfigurations.
  16. Remediation Steps: Google would have to review IAM policies and repository configurations to ensure that only intended users have access. It likely involved auditing existing repositories for similar exposures and educating users on proper access control settings.

Key Takeaways:

  1. Access Control Vigilance: Properly configured IAM policies are crucial to ensure that resources like repositories are not unintentionally exposed.
  2. Continuous Monitoring: Regular audits and monitoring for access control misconfigurations can prevent such exposures. Automated tools should be implemented to flag and correct such issues promptly.
  3. Security Awareness: Teams must be educated and continuously reminded of the importance of setting proper access controls whenever creating or modifying repositories.
  4. Error Message Handling: Informative error messages can inadvertently assist attackers in enumerating resources or access levels. They should be carefully designed to avoid leaking sensitive information.
  5. Strengthening Internal Security Programs: Ensuring that a robust responsible disclosure program is in place to encourage reporting and quick remediation of discovered vulnerabilities.

Conclusion:

This write-up underscores the critical importance of vigilant access control configurations and continuous monitoring within cloud environments. Misconfigurations can lead to significant security breaches, emphasizing the need for strict IAM policy management and regular auditing. The responsible disclosure and quick remediation by both Berner and Google are commendable, ensuring that such oversights are swiftly addressed.

For full details, check the original Medium post here.