Detailed Technical Analysis of "Dropping a Shell in GKE (Google Kubernetes Engine)"

Overview:
Ezequiel Pereira’s write-up explores a security vulnerability within Google Kubernetes Engine (GKE) that allowed attackers to gain unauthorized shell access to an internal environment. It highlights how misconfigurations and lack of proper isolate checks can lead to severe security breaches within managed Kubernetes services.

Key Technical Details:

1. Initial Discovery:
   The researcher discovered that by using limited privileged access, he could escalate privileges within a GKE environment. By examining public resources, Ezequiel identified a potential attack vector within GKE’s usage of IAM (Identity and Access Management) roles and service accounts.

2. IAM Roles and Service Account Misconfiguration:

3. Service Accounts: GKE uses service accounts tied to specific GCP (Google Cloud Platform) roles. A misconfigured service account with elevated privileges can be exploited to perform actions beyond its intended scope.

4. IAM Role Exploitation: The researcher found that obtaining a token from a service account with elevated privileges could be used to assume other roles or service accounts within the same GCP project. This token could then be leveraged to gain access to additional resources.

5. Gaining Command Execution:

6. Exploiting Workloads: Through a compromised service account, the attacker can exploit workloads running within the GKE environment. By interacting with Kubernetes' API server, the attacker could deploy a pod or job, effectively gaining a foothold in the environment.

7. Deploying Malicious Pods: Ezequiel demonstrated that by creating and deploying a pod, he could execute commands leading to unauthorized shell access. This highlights a critical flaw where the Kubernetes RBAC (Role-Based Access Control) settings were inadequate.

8. Persistence and Lateral Movement:

9. Shell Access: Once a shell was obtained, the attacker could explore the internal network, potentially identifying additional vulnerabilities or misconfigurations.

10. Escalation through Privileges: The researcher showed that with sufficient exploration, further escalation could be achieved. By navigating through internal resources and exploiting further IAM role assumptions, broader access to internal assets was possible.

11. Key Lessons and Mitigation Strategies:

12. RBAC Best Practices: Implement strict RBAC policies to ensure that service accounts and roles have the least privileges necessary.
13. Service Account Management: Regular auditing of service accounts and their permissions can help mitigate such vulnerabilities. Unnecessary privileges should be revoked, and services running under an account should be the minimal code required to perform their roles.
14. Network Policies & Isolation: Deploy network policies to isolate workloads and restrict unauthorized lateral movement. Ensuring proper segmentation between services and monitoring any deviations from expected behavior.
15. Monitoring and Alerting: Use logging, monitoring, and alerting mechanisms to detect unauthorized access or unusual activity within the environment. Tools like Stackdriver can be helpful to identify anomalies.

Key Takeaways:

• Exploiting Privileges: A misconfigured service account with elevated permissions can be a significant security risk in a Kubernetes environment. Always audit and minimize the privileges of service accounts.
• Gaining Shell Access: Compromising internal credentials can lead to the deployment of malicious pods, providing an attacker with shell access, and highlighting inadequate RBAC policies.
• Persistence and Lateral Movement: Once inside, an attacker can use persistence techniques and lateral movement strategies to escalate privileges and gain broader access to internal resources.
• Mitigation: RBAC best practices, stringent service account management, robust network policies, and comprehensive monitoring are critical to mitigating such attack vectors.

Conclusion:

Ezequiel Pereira’s write-up sheds light on the importance of securing Kubernetes environments, especially within managed services like GKE. Proper IAM role configurations, strict RBAC policies, network segmentation, and continuous monitoring are essential to protect against unauthorized access and privilege escalation attacks.

For the full technical writeup, refer to the original blog post here.