Over the weekend, Microsoft released details of a zero-day vulnerability (CVE-2014-1776) present in all versions of Internet Explorer from IE 6 through IE 11. The vulnerability is a use-after-free when the browser attempts to make property changes for HTML elements within a page containing VML. Although VML was officially deprecated as of IE 10, HTML pages can use special syntax to force current versions of the browser to render as if it was using an earlier browser version. This syntax looks like:
When used in a current browser, such as IE 11, the page will render as if it were being loaded in IE 9. So don't always assume just because you're running a newer version of the browser that you are not vulnerable!
We received some early detection guidance from Microsoft, and spent the evening Saturday developing two filters to address this attack. 13902 is a vulnerability filter which should have minimal false positive potential and will address the root cause of the use-after-free vulnerability. 13903 is a policy filter which will be prone to false positives, but can detect the use of VML in a web page - a component critical to this attack.
In order to provide the most complete coverage for this vulnerability, our security researchers analyzed the proof-of-concept file from Microsoft and made a number of modifications to it. This included trimming the attack down to its essential elements needed to cause the crash, modifying which objects and methods were critical to the bug, and addressing multiple ways of triggering the vulnerability.
Finally, the Department of Homeland Security has issued the following release, recommending against the use of Internet Explorer until such time the vulnerability can be patched.
We will continue to monitor the threat landscape for public use of this exploit. If you experience hits on filter 13902 and are able to obtain a trace, please contact HP TippingPoint TAC for confirmation. Thank you!