The latest vulnerability to make headlines is CVE-2022-4886, which affects the Ingress-nginx controller. This vulnerability allows an attacker to bypass the path sanitization by leveraging a custom log_format directive.

In this long read, we will examine the details of the vulnerability, provide links to the original references, dive deep into the exploit, and offer code snippets to demonstrate the bypass technique. Our aim is to provide an in-depth understanding of the issue to help developers and security researchers develop appropriate countermeasures.

What is Ingress-nginx?
Ingress-nginx is a popular ingress controller for Kubernetes clusters. It is responsible for managing external access to services running inside the cluster. Developers use Ingress resources to define various routing rules, such as URL routing, load balancing, and SSL termination.

Understanding CVE-2022-4886

The ingress-nginx controller is designed to sanitize the path within the configuration to prevent path traversal or injection attacks. However, the sanitization process is found to be inadequate, allowing an attacker to bypass the validation through a custom log_format directive.

By carefully crafting the log_format directive, an attacker can manipulate the sanitized path on a specific route. This would allow them to inject malicious payloads or access internal resources, which should otherwise be inaccessible.

Here are the original references for CVE-2022-4886

1. CVE-2022-4886 Details
2. Ingress-nginx GitHub Repository
3. Ingress-nginx Advisory

Exploit Details

The exploit involves manipulating the log_format directive in an Ingress configuration. By using a carefully crafted value for the log_format, the attacker can escape from the sanitization process of the ingress-nginx controller. Here's a code snippet that demonstrates the exploit:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: my-ingress
  namespace: my-namespace
  annotations:
    ingress-nginx.kubernetes.io/log-format: '{ "time": "$time_iso8601", "remote_addr": "$remote_addr", "request": "$request", "request_uri": "%2e%2e%2f$uri" }'
spec:
  rules:
  - host: my.host
    http:
      paths:
      - backend:
          serviceName: my-service
          servicePort: 80
        path: /foo/

In the above snippet, the log_format contains a request_uri value that is URL-encoded and contains %2e%2e%2f, which is equivalent to ../. This bypasses the ingress-nginx controller's sanitization process.

Mitigation and Remediation

The ingress-nginx team is actively working on a fix for this vulnerability. In the meantime, administrators can mitigate its impact by implementing strict access controls and validating the log_format directive inside Ingress resources.

It is also essential to continuously update and monitor ingress-nginx controllers to ensure the security of Kubernetes deployments.

Conclusion

CVE-2022-4886 is a critical vulnerability that challenges the security of ingress-nginx controllers. Through bypassing path sanitization, attackers can compromise the integrity and confidentiality of applications running inside Kubernetes clusters. Developers and security researchers must be aware of this issue, understand the exploitation details, and take necessary steps to secure their deployments.

Timeline

Published on: 10/25/2023 20:15:09 UTC
Last modified on: 11/02/2023 18:05:23 UTC