Following Cyberis’ recent articles on bypassing perimeter filtering devices (e.g. proxies, IDS and next-generation firewalls) by manipulating HTTP response headers, we’ve taken a closer look at some more obscure Content-Encoding mechanisms. This article discusses Shared Dictionary Compression over HTTP (SDCH), and the implications for perimeter security controls designed to protect your network from unwanted content.
Ever wondered if your web traffic is being silently intercepted by a transparent proxy? Chances are if you are running on mobile broadband your provider will be saving bandwidth, by rerouting your traffic to cache content and perform image compression. You may come across transparent proxies used for logging purposes, AUP enforcement and sometimes evil (http://www.ex-parrot.com/pete/upside-down-ternet.html - the old trick of inverting all images on a web page).