A proxy is an intermediary server that handles communication between a client and a destination server. In security contexts, proxies serve dual purposes: defenders use them to filter traffic, enforce policies, and inspect content, while security testers use intercepting proxies to analyze and manipulate application traffic during assessments.
How It Works
Forward proxies sit between internal users and the internet, forwarding outbound requests on behalf of clients. Organizations deploy forward proxies to enforce acceptable use policies, block access to malicious domains, inspect encrypted traffic for threats, and log web activity for audit purposes. The client is aware of the proxy and directs traffic through it, either through explicit configuration or transparent interception.
Reverse proxies sit in front of web servers, receiving inbound requests from the internet and forwarding them to the appropriate backend server. They provide load balancing, SSL termination, caching, and an additional security layer that can filter malicious requests before they reach the application. Web application firewalls often operate as reverse proxies, inspecting each request against a set of rules before deciding whether to forward or block it.
Intercepting proxies are the primary instruments used during security testing. They sit between the tester's browser and the target application, capturing every request and response in real time. The tester can pause requests, modify parameters, replay them with different values, and observe how the application responds to unexpected input. This manual inspection capability is essential for discovering business logic flaws, authentication bypasses, and access control weaknesses that automated scanners cannot detect.
Why It Matters
Proxies are foundational to both security defense and security testing. Misconfigured proxies can introduce vulnerabilities, such as open proxies that allow anyone to route traffic through them, or reverse proxies that fail to forward security headers. Understanding how proxies handle requests is critical because discrepancies between proxy behavior and application behavior frequently create exploitable gaps in security controls.
Need your application tested? Get in touch.