SIP Server Enumeration Scanner

Enumerates a SIP server's valid extensions (users).

The script works by sending REGISTER SIP requests to the server with the specified extension and checking for the response status code in order to know if an extension is valid. If a response status code is 401 or 407, it means that the extension is valid and requires authentication. If the response status code is 200, it means that the extension exists and doesn't require any authentication while a 403 response status code means that extension exists but access is forbidden. To skip false positives, the script begins by sending a REGISTER request for a random extension and checking for response status code.