http-litespeed-sourcecode-download.nse exploits a null-byte poisoning vulnerability in Litespeed Web Servers 4.0.x before 4.0.15 to retrieve the target script's source code by sending a HTTP request with a null byte followed by a .txt file extension (CVE-2010-2333).
If the server is not vulnerable it returns an error 400. If index.php is not found, you may try /phpinfo.php which is also shipped with LiteSpeed Web Server. The attack payload looks like this:
* <code>/index.php\00.txt</code>
References:
* http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2010-2333
* http://www.exploit-db.com/exploits/13850/