This blog post is part of series of two posts that describe weaknesses in Microsoft Excel that could be leveraged to create malicious phishing documents signed by Microsoft that load arbitrary code.
These weaknesses have been addressed by Microsoft in the following patch: CVE-2021-28449. This patch means that the methods described in this post are no longer applicable to an up-to-date and securely configured MS Office install. However, we will uncover a largely unexplored attack surface of MS Office for further offensive research and will demonstrate practical tradecraft for exploitation.
In this blog post (part 1), we will discuss the following:
- The Microsoft Analysis ToolPak Excel and vulnerabilities in XLAM add-ins which are distributed as part of this.
- Practical offensive MS Office tradecraft which is useful for weaponizing signed add-ins which contain vulnerabilities,