Use-after-free error was disclosed in Microsoft Office Excel 2007, 2010 and 2013. The vulnerability allows remote code execution when the victim opens a malicious .xlsb file. This file can be delivered via email or during internet surfing.
The vulnerability was disclosed by Zero Day Initiative, a security company recently acquired by HP. ZDI-15-639 contains brief description of this vulnerability.
We have tested the provided PoC codes against Microsoft Excel 2013 and confirm successful crash of Microsoft Excel. Further investigation may show if the vulnerability could be used to execute arbitrary code in the latest version of Microsoft Office.
Our analysis shows that, combined with recent generic ASLR bypass in Microsoft Office and publicly disclosed PoC codes, public exploitation of this vulnerability is highly possible in the nearest future.