In October 2021 I was researched ingress-nginx for possibility to bypass external authentication using path traversal. It was origin story for other investigations regarding insecure usage of $request_uri which leaded to Apache APISIX CVE-2021-43557.

To successful bypass access control using path traversal in $request_uri, you need to have buggy authentication/authorization service. Buggy in a way it’s not normalizing url/uri that is part of access control decision. Let me find more of those on github that are relying on X-Original-Url.

In this article, I will extend topic by bug bounty tips for weaknesses in authentication/authorization implementation in relation to nginx’s $request_uri variable. APIs This vulnerability is for APIs. Best scenario are microservice deployed to Kubernetes and exposed by ingress controller.

In this part I will research another ingress controller based on nginx: 🦍 kong. At the end of article I will mention in short F5 NGINX Ingress Controller. In kong there is no explicit feature called external authentication, but developers gave possibility to create it using plugins.