browserrecon – Passive Browser Fingerprinting

May 14, 2008 – 6:00 AM

Most of todays tools for fingerprinting are focusing on server-side services. Well-known and widely-accepted implementations of such utilities are available for http web services, smtp mail server, ftp servers and even telnet daemons. Of course, many attack scenarios are focusing on server-side attacks.

Client-based attacks, especially targeting web clients, are becoming more and more popular. Browser-targeted attacks, drive-by pharming and web-based phishing provide a broad aspect of threats during surfing in the world wide web. Attacker might initialize and optimize their attacks by fingerprinting the target application to find the best possible way to compromise the client.

The browserrecon project is going to prove, that client-side fingerprinting is possible and useful too. In this particular implementation, currently available in php only, the given web browser is identified by the used http requests. Similar to the http fingerprinting provided within httprecon ( the header lines and values are analyzed and compared to a fingerprint database.

The current implementation of browserrecon is provided as a php script and ready for live testing on the project web site. However, all web-based scripting languages that are able to access the http headers sent by the client are able to provide the same functionality. Further ports to ASP.NET, JSP and classic CGI are possible. Even the web server itself or an inline device (e.g. a sniffer or a firewall) might be able to do the same fingerprinting of the http request behavior.

A very similar approach for client-side application fingerprinting can be applied to other services and clients too. For example mail clients can be identified by their individual smtp and pop3 command chains. Or ftp clients might be determined by their specific command sequences.


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