SIP (Session Initiation protocol) is commonly used for real time communication, such as instant messaging and voice communication. The product under test is VOIP monitor, which is a listening software for VOIP messages.
Where ever there is user input being handled or controlled, XSS may be possible! On the main VOIP listener message, there is an XSS bug in the User-Agent header. By sending VOIP messages with an XSS payload in the User-Agent header, the administrative account can be forced to perform arbitrary actions.
The author takes this from XSS to control over the application. Using custom SQL queries (which for some reason is allowed from the admin-side), another administrative user can be created on the application, a keylogger can be added... With XSS on the admin page, it is essentially game over.
Where ever there is user input being displayed, XSS may be possible! Sanitizing all inputs is crucial from preventing this types of bugs.