A new Kubernetes vulnerability, CVE-2024-7646, has recently been identified and demands urgent attention from security professionals and DevOps teams. This vulnerability severely threatens the security of systems using the widely adopted ingress-nginx controller, potentially allowing attackers to bypass annotation validation and gain unauthorized access to critical cluster resources.

Attackers can exploit this vulnerability by injecting malicious annotations that bypass security checks. This can lead to severe consequences, such as command injection granting attackers control over the entire cluster. These malicious annotations can also disrupt the ingress-nginx controller’s operations, causing service outages and degraded performance. Additionally, this vulnerability exposes sensitive credentials and secrets, allowing attackers to access and exfiltrate them.

The CVE-2024-7646 vulnerability underscores critical aspects of Kubernetes security: the need for solid validation mechanisms to secure annotations, the importance of protecting the software supply chain given the widespread use of essential components like ingress-nginx, and the value of adopting a zero trust architecture to mitigate risks from both internal and external threats.

With a CVSS v3.1 base score of 8.8, this high-risk vulnerability seriously threatens the confidentiality, integrity, and availability of affected systems. Immediate action is crucial to prevent significant damage, making it a top priority. Security teams and DevOps professionals should promptly apply patches, closely monitor systems, and take proactive measures to protect sensitive data and resources in complex Kubernetes environments.

Resolution

To resolve the CVE-2024-7646 vulnerability in Kubernetes environments using ingress-nginx, it’s critical to take immediate steps:

1. Upgrade Ingress-NGINX: The most effective measure is to upgrade ingress-nginx to version 1.11.2 or higher. This version contains the necessary security patches to mitigate the vulnerability, preventing attackers from exploiting the annotation validation bypass.
2. Restrict Annotations: Explicitly disallow the nginx.ingress.kubernetes.io/server-snippet annotation to further safeguard your system. This step ensures that no unauthorized or potentially malicious configurations can be injected.
3. Enforce TLS Client Verification: Set the auth-tls-verify-client annotation to either ‘on,’ ‘off,’ ‘optional,’ or ‘optional_no_ca’ values. This enforces stricter control over TLS client authentication, reducing the attack surface by ensuring that only correctly authenticated clients can interact with your services.

Implementing these steps can address the immediate threat posed by CVE-2024-7646 and enhance the overall security posture of your Kubernetes clusters. Review and update security configurations regularly to stay ahead of emerging threats.

Kyverno is an open-source policy engine built to enforce policies and ensure compliance within Kubernetes environments. In the context of the CVE-2024-7646 vulnerability, organizations can leverage Kyverno to implement policies that block malicious annotations quickly, restrict access to sensitive resources, and prevent unauthorized command execution. This helps mitigate the risks posed by the vulnerability and ensures the integrity and security of the affected Kubernetes clusters.

Nirmata Policy Manager (NPM), built on Kyverno, enhances this by providing a centralized, user-friendly interface for policy deployment and enforcement across clusters. To address CVE-2024-7646, NPM allows the implementation of a targeted policy that mitigates the vulnerability and provides a detailed overview of all affected instances across the cluster fleet. This aligns with the Shift-Down approach by applying consistent and automated security measures, ensuring comprehensive protection and oversight at scale.

Using NPM ensures effective policy enforcement and governance, helping organizations quickly address vulnerabilities like CVE-2024-7646 and maintain a strong security posture.

Mitigation at Scale

The following policy that verifies your ingress-nginx is updated to version 1.11.2 or higher, disallows the use of the nginx.ingress.kubernetes.io/server-snippet annotation, and ensures the auth-tls-verify-client annotation is set to ‘on,’ ‘off,’ ‘optional,’ or ‘optional_no_ca.’

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: enforce-ingress-nginx-controller-version-and-annotation-policy
spec:
  validationFailureAction: Enforce
  background: true
  rules:
  - name: validate-ingress-annotations
	match:
  	resources:
    	kinds:
    	- Ingress
	validate:
  	message: "The annotation nginx.ingress.kubernetes.io/server-snippet is not allowed."
  	pattern:
    	metadata:
      	annotations:
        	X(nginx.ingress.kubernetes.io/server-snippet): ""
  - name: validate-auth-tls-verify-client
	match:
  	resources:
    	kinds:
    	- Ingress
	validate:
  	message: "auth-tls-verify-client annotation must be 'on', 'off', 'optional', or 'optional_no_ca'."
  	deny:
    	conditions:
      	any:
      	- key: "{{request.object.metadata.annotations.\"nginx.ingress.kubernetes.io/auth-tls-verify-client\"}}"
        	operator: AnyNotIn
        	value:
        	- "on"
        	- "off"
        	- "optional"
        	- "optional_no_ca"
  - name: ensure-ingress-nginx-controller-version-pattern
	match:
  	resources:
    	kinds:
      	- Pod
	validate:
  	message: "The ingress-nginx controller image version must start with v1.11."
  	pattern:
    	spec:
      	containers:
        	- name: controller
          	image: "registry.k8s.io/ingress-nginx/controller:v1.11.*"

  - name: deny-lower-ingress-nginx-controller-versions
	match:
  	resources:
    	kinds:
      	- Pod
	validate:
  	message: "The ingress-nginx controller image version must be v1.11.2 or greater."
  	deny:
    	conditions:
      	- key: "{{ request.object.spec.containers[?(@.name=='controller')].image }}"
        	operator: AnyIn
        	value:
          	- "registry.k8s.io/ingress-nginx/controller:v1.11.0"
          	- "registry.k8s.io/ingress-nginx/controller:v1.11.1"
          	- "registry.k8s.io/ingress-nginx/controller:v1.10.*"
          	- "registry.k8s.io/ingress-nginx/controller:v1.9.*"
          	- "registry.k8s.io/ingress-nginx/controller:v1.8.*"
          	- "registry.k8s.io/ingress-nginx/controller:v1.7.*"
          	- "registry.k8s.io/ingress-nginx/controller:v1.6.*"
          	- "registry.k8s.io/ingress-nginx/controller:v1.5.*"
          	- "registry.k8s.io/ingress-nginx/controller:v1.4.*"
          	- "registry.k8s.io/ingress-nginx/controller:v1.3.*"
          	- "registry.k8s.io/ingress-nginx/controller:v1.2.*"
          	- "registry.k8s.io/ingress-nginx/controller:v1.1.*"
          	- "registry.k8s.io/ingress-nginx/controller:v1.0.*"

Nirmata Policy Manager provides robust capabilities and features for deploying and enforcing security policies across Kubernetes clusters, making it an effective tool for addressing vulnerabilities like CVE-2024-7646. Here’s how to utilize NPM to handle this issue:

1. Developing a Security Policy: Create a policy specifically designed to address CVE-2024-7646. This policy should mandate upgrading ingress-nginx to version 1.11.2 or higher, disallow unsafe annotations such as nginx.ingress.kubernetes.io/server-snippet, and ensure the auth-tls-verify-client annotation is set correctly.
2. Implement the Policy: Apply the security policy to the clusters that use ingress-nginx, or deploy it across all clusters in your environment to ensure comprehensive protection.
3. Automate Policy Enforcement:  Nirmata Policy Manager will automatically enforce the policy across your clusters, immediately mitigating the vulnerabilities associated with CVE-2024-7646.
4. Monitor and Audit: Implement real-time monitoring to ensure policy compliance. NPM will generate detailed audit reports to track policy enforcement, detect deviations, and provide insights into your security status.
5. Remediate Non-Compliant Clusters: NPM can automatically address non-compliant clusters by enforcing the policy, ensuring all clusters adhere to the required security measures.