Transparent Proxy Abuse presented at OWASP Appsec 2009

by Robert Auger (PayPal),

Tags: Security Web Monitoring


Summary : Transparent proxies allow organizations to influence and monitor the traffic from its users without their knowledge or participation. Transparent proxies act as intermediaries between a user and end destination, and aren't generally apparent to users sitting behind them. Enterprises, Hotels, and Internet Service Providers often use transparent proxy products to lower bandwidth consumption, speed up page loads for their users, and for monitoring and filtering of web surfing. When certain transparent proxy architectures are in use an attacker can achieve a partial Same Origin Policy Bypass resulting in access to any host reachable by the proxy via the use of client plug-in technologies (such as Flash, Applets, etc) with socket capabilities. This write up will describe this architecture, how it may be abused by Flash, its existence in various network layouts, and mitigations.

Robert Auger: Robert Auger serves as a Information Security Engineer on the secure development team under PayPal's Information Risk Management group. In this role, Robert co-develops PayPal's SDLC and security testing strategies. Robert is also a co-founder and officer of The Web Application Security Consortium (, moderates The Web Security Mailing List (, leads the WASC Threat Classification Project (, and runs CGISecurity, an application security news portal.