source: https://www.securityfocus.com/bid/7387/info

BadBlue is prone to a vulnerability that could allow remote attackers to gain unauthorized access. This is due to an input validation issue in the 'ext.dll' component that could allow a remote attacker to cause '.hts' files to be interpreted by the server. This could lead to unauthorized execution of administrative commands. 

http://www.example.com/ext.dll?MfcIsapiCommand=LoadPage&page=admin.hts%20&a0=add&a1
=root&a2=%5C