In addition to the previously mentioned Nmap script, GuestStealer has now made its way into a Nessus plugin and a Metasploit module. Nessus Plugin 44646 was released by Tenable a few weeks ago and the Metasploit module was pushed up to the trunk last week.
GuestStealer has been mentioned in several articles and blog posts recently, including DarkReading – Tech Insight: Securing The Virtualized Server Environment and The Hacker News Network. While most have been accurate, several early blogs stated that GuestStealer used a cross site scripting attack to steal the guests. So to clarify and avoid any confusion, GuestStealer exploits the directory traversal vulnerability described in CVE-2009-3733. For further information, check out the presentation slides.