During a recent application penetration test on behalf of a client, one of the security vulnerabilities discovered was a stored cross-site scripting vector, delivered via a JSON request to a MVC3 controller. The malicious data (in this case a simple script tag proof-of-concept) was written to the database and subsequently echoed back to the user when viewing a number of pages within the application.
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.