I thought that after the success of MoBB last year, fuzzing browsers will be pointless, since all vendors would take care of the easily-found bugs before a release. It turns out that I was wrong. I ran a very simple ActiveX fuzzer against Vista and found a NULL pointer dereference bug in no time. The vulnerable ActiveX control is on the pre-approved list in IE7, which makes the bug easy to trigger with no security warnings and no user interaction. Try this: <script language="JavaScript"> obj = new ActiveXObject("giffile"); obj.bgColor; </script> MSRC said that this is a reliability bug and not a security issue, and it will be fixed at some point in the future. I agree that DoS bugs against IE are not very important (as long as skape doesn't drop any more vulns like MS06-051 :-), but it's interesting that such a simple bug in such an obvious part of the IE7 attack surface was not discovered and fixed before the release. See the full technical details at http://www.determina.com/security.research/vulnerabilities/activex-bgcol or.html More about fuzzers and ActiveX at http://determina.blogspot.com/2007/01/fuzzing-shouldnt-work.html Alexander Sotirov Determina Security Research