Multiple browsers Windows mailto protocol Office 2003 file attachment exploit: Application protocols handling in Microsoft Windows is badly designed, i.e. when someone types mailto:someone@somewhere.com into a browser the protocol is first looked up under HKEY_CLASSES_ROOT\%protocol%\shell\open\command, if it is a protocol that is allowed under the current user context then the value is simply replaced by the contents in the address bar at %1.
e9d335bf8d915cd060f8c111a59da1d0d42a6dbbbd5cadd09f58e5c92e11646f