DescriptionOpen a new tab, and then open the Developer Tools by pressing F12, or selecting it from the "Tools" menu. Then select the "Scripts" tab in the Developer Tools window. Next hover the mouse over one of the buttons with the text "Start Debugging", "Run Script" and "Multi Line Mode"/"Single Line Mode". When a tooltip is shown, click the button.At this point, memory that was freed is accessed. When running MSIE with page heap enabled, you will see an access violation exception.
ExploitBecause the attacker vector appears highly unlikely to represent a risk to any user, I did not bother to do an in-depth investigation. However, the use-after- free occurs in the same process in which the web-page is rendered. This suggests that there may be a way for the web-page to reallocate the freed memory before its reuse and potentially exploit this issue. However, it appears that the free and re-use occur in a very short time span, which would make that rather hard if not impossible.
NotesI allow vendors 60 days to fix an issue, unless they can provide an adequate reason for extending this deadline. Failure to meet a deadline without an adequate explanation will normally result in public disclosure of information regarding the vulnerability to the general public.
Timeline23 January 2015: vulnerability discovered and reported to MSRC by email.
23 January 2015: email from MSRC acknowledges receipt of report.
25 March 2015: email to MSRC to notify them that deadline has been exceeded.
25 March 2015: Full disclosure of vulnerability details.