CVE-2022-2385: Kubernetes Aws-iam-authenticator Privilege Escalation

CVE-2022-2385 Overview

A privilege escalation vulnerability was discovered in aws-iam-authenticator, a Kubernetes authentication component that integrates with AWS IAM. This security issue allows an allow-listed IAM identity to modify their username and escalate privileges within the Kubernetes cluster. The vulnerability stems from improper input validation in the authentication flow, enabling authenticated users to potentially gain unauthorized access to cluster resources.

Critical Impact

Allow-listed IAM identities can modify their username during authentication, potentially escalating privileges to higher-privileged roles within the Kubernetes cluster.

Affected Products

• Kubernetes aws-iam-authenticator

Discovery Timeline

• 2022-07-12 - CVE CVE-2022-2385 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-2385

Vulnerability Analysis

This vulnerability affects the Kubernetes aws-iam-authenticator component, which is responsible for authenticating users to Kubernetes clusters using AWS IAM credentials. The core issue lies in improper input validation (CWE-20) during the authentication process, where the authenticator fails to properly validate or sanitize the username parameter provided by IAM identities.

When an IAM identity is allow-listed for cluster access, the authenticator should enforce strict mapping between the IAM identity and the corresponding Kubernetes username. However, due to this vulnerability, an authenticated IAM identity can manipulate the username field during the authentication flow. This allows attackers who already have some level of cluster access to impersonate other users or roles, effectively bypassing the intended access control mechanisms.

The network-accessible nature of this vulnerability means that any authenticated user with network access to the Kubernetes API server can potentially exploit this flaw. The attack requires low privileges (an existing allow-listed IAM identity) and no user interaction, making it relatively straightforward to exploit once the prerequisites are met.

Root Cause

The root cause is improper input validation (CWE-20) in the aws-iam-authenticator's handling of username parameters. The authenticator fails to enforce strict validation of the username mapping, allowing allow-listed IAM identities to specify or modify their username during the authentication process. This lack of validation enables the bypass of intended identity-to-username mappings configured by cluster administrators.

Attack Vector

The attack is network-based and can be executed by any allow-listed IAM identity with access to the Kubernetes cluster. The attacker leverages their existing IAM credentials to authenticate to the cluster, but manipulates the authentication request to modify their assigned username. By impersonating a higher-privileged user or a user with broader permissions, the attacker can escalate their privileges within the cluster.

The attack requires:

1. An existing allow-listed IAM identity (low privilege requirement)
2. Network access to the Kubernetes API server
3. Knowledge of target usernames or roles to impersonate

The exploitation does not require user interaction, making it suitable for automated attacks. Successful exploitation can lead to complete compromise of confidentiality, integrity, and availability of cluster resources.

Detection Methods for CVE-2022-2385

Indicators of Compromise

• Unusual authentication patterns where IAM identities authenticate as different Kubernetes users than expected
• Discrepancies between IAM identity ARNs and the Kubernetes usernames in audit logs
• Unexpected access to cluster resources by users who should not have permissions

Detection Strategies

• Enable and monitor Kubernetes audit logs for authentication events involving aws-iam-authenticator
• Compare IAM identity ARNs in authentication requests against the expected username mappings in ConfigMap
• Alert on any authentication attempts where the claimed username does not match the configured mapping for the IAM identity

Monitoring Recommendations

• Implement centralized logging for all Kubernetes API server authentication events
• Create alerts for privilege escalation patterns, such as users suddenly accessing resources outside their normal scope
• Regularly review aws-iam-authenticator ConfigMap configurations to ensure proper IAM-to-username mappings

How to Mitigate CVE-2022-2385

Immediate Actions Required

• Update aws-iam-authenticator to the latest patched version immediately
• Audit existing IAM identity mappings in your aws-iam-authenticator ConfigMap
• Review Kubernetes audit logs for any suspicious authentication activity that may indicate past exploitation
• Implement additional RBAC restrictions to limit the blast radius of potential privilege escalation

Patch Information

Refer to the GitHub Issue #472 for detailed patch information and affected version ranges. The Google Groups Discussion contains additional context from the Kubernetes security team regarding the vulnerability disclosure and remediation guidance.

Workarounds

• Implement strict network policies to limit access to the Kubernetes API server to trusted networks only
• Reduce the number of allow-listed IAM identities to minimize the attack surface
• Enable and enforce additional authentication mechanisms alongside aws-iam-authenticator where possible
• Implement strict RBAC policies with least-privilege principles to limit the impact of potential username manipulation

# Review current IAM mappings in aws-iam-authenticator ConfigMap
kubectl get configmap aws-auth -n kube-system -o yaml

# Enable audit logging for authentication events
# Add to kube-apiserver configuration
# --audit-policy-file=/etc/kubernetes/audit-policy.yaml
# --audit-log-path=/var/log/kubernetes/audit.log