CVE-2024-7646: Ingress-Nginx Auth Bypass Vulnerability

CVE-2024-7646 Overview

A critical security vulnerability has been discovered in Kubernetes ingress-nginx that allows authenticated attackers to bypass annotation validation mechanisms and inject arbitrary commands. This command injection vulnerability enables malicious actors with permission to create Ingress objects (in the networking.k8s.io or extensions API group) to obtain the credentials of the ingress-nginx controller, which in the default configuration has access to all secrets in the cluster.

Critical Impact

Attackers can leverage this vulnerability to gain access to the ingress-nginx controller credentials, potentially compromising all secrets stored in the Kubernetes cluster and enabling lateral movement across the entire infrastructure.

Affected Products

• Kubernetes ingress-nginx controller (unpatched versions)
• Kubernetes clusters using default ingress-nginx configurations
• Environments where users have Ingress object creation permissions

Discovery Timeline

• August 16, 2024 - CVE-2024-7646 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-7646

Vulnerability Analysis

This vulnerability stems from improper input validation (CWE-20) in the ingress-nginx controller's annotation handling mechanism. The ingress-nginx controller processes annotations attached to Kubernetes Ingress objects to configure NGINX behavior. An attacker with permissions to create or modify Ingress objects can craft malicious annotations that bypass the existing validation checks, allowing them to inject arbitrary commands that execute within the context of the ingress-nginx controller.

The attack is particularly dangerous because it exploits a fundamental trust assumption in Kubernetes RBAC - that users authorized to create Ingress objects should be limited to defining routing rules, not executing commands on the controller. The vulnerability breaks this security boundary.

Root Cause

The root cause lies in insufficient validation of annotation values within the ingress-nginx controller. When processing Ingress object annotations, the controller fails to properly sanitize or validate certain input patterns, allowing specially crafted annotation values to escape the intended context and execute arbitrary commands. This improper input validation allows attackers to inject shell metacharacters or command sequences that are subsequently interpreted by the underlying system.

Attack Vector

The attack is network-accessible and requires low privileges - specifically, an attacker needs only the ability to create or modify Ingress objects within the Kubernetes cluster. This permission is commonly granted to developers and application teams in multi-tenant Kubernetes environments.

The exploitation flow involves:

1. An attacker creates or modifies an Ingress object with malicious annotation values
2. The ingress-nginx controller processes the Ingress object
3. The validation bypass allows the injected commands to execute
4. The attacker obtains the controller's credentials, which typically have access to all cluster secrets

This attack requires no user interaction and can be executed remotely through the Kubernetes API.

Detection Methods for CVE-2024-7646

Indicators of Compromise

• Unusual Ingress object creation or modification events with suspicious annotation values containing shell metacharacters
• Unexpected command execution or processes spawned by the ingress-nginx controller pod
• Anomalous access patterns to Kubernetes secrets from the ingress-nginx service account
• Log entries indicating annotation parsing errors or unexpected controller behavior

Detection Strategies

• Monitor Kubernetes audit logs for Ingress object creation and modification events, particularly those with unusual annotation patterns
• Implement admission controllers to validate and sanitize Ingress annotations before they reach the ingress-nginx controller
• Deploy runtime security monitoring within the ingress-nginx controller pod to detect command injection attempts
• Review and alert on any attempts to access cluster secrets outside of normal operational patterns

Monitoring Recommendations

• Enable detailed audit logging for all Ingress-related API operations in Kubernetes
• Configure alerting for unexpected shell command execution within the ingress-nginx controller namespace
• Monitor network traffic originating from ingress-nginx pods for suspicious outbound connections
• Implement anomaly detection for secret access patterns in your Kubernetes environment

How to Mitigate CVE-2024-7646

Immediate Actions Required

• Update ingress-nginx controller to the latest patched version immediately
• Review all existing Ingress objects for suspicious or unexpected annotations
• Audit RBAC policies to ensure Ingress creation permissions follow the principle of least privilege
• Consider implementing admission webhooks to validate Ingress annotations before processing

Patch Information

The Kubernetes security team has addressed this vulnerability through patches available in the ingress-nginx repository. Administrators should review the official patches documented in GitHub Pull Request #11719 and GitHub Pull Request #11721. Additional details are available in Kubernetes Issue #126744 and the Kubernetes Security Announcement.

Workarounds

• Restrict Ingress object creation permissions to only trusted administrators until patches can be applied
• Implement custom admission controllers that strictly validate all Ingress annotations against an allowlist
• Consider temporarily disabling or limiting the annotations that the ingress-nginx controller processes
• Deploy network policies to limit the blast radius if the controller is compromised

# Example: Restrict Ingress creation to admin namespace only
kubectl create clusterrole ingress-admin --verb=create,update,patch --resource=ingresses
kubectl create clusterrolebinding ingress-admin-binding --clusterrole=ingress-admin --group=cluster-admins
# Review existing ingress objects for suspicious annotations
kubectl get ingress --all-namespaces -o jsonpath='{range .items[*]}{.metadata.namespace}/{.metadata.name}: {.metadata.annotations}{"\n"}{end}'