The vulnerability was discovered by researcher Fermin J. Serna, a former Microsoft security engineer. It takes advantage of the way that IE handles some command line options in certain conditions. The ElevationPolicy in IE will treat the Microsoft Diagnostic Tool (msdt.exe) as a medium-integrity process if the user requests it to do so. If the user clicks the continue button on the dialog box, his code will run and he s escaped the sandbox in the browser. executing the attack would be trivial under the right conditions.
Source: https://threatpost.com/jumping-out-of-ies-sandbox-with-one-click/102054/