In the previous post I demonstrated how to bypass Microsoft’s RFG, a.k.a. “Shadow Stack”, assuming we can locate the shadow stack. In this post I’ll fill up the missing details, and will describe how to find “Shadow” memory sections in a process’s virtual address space. While the technique works both in Windows and Linux, and it will demonstrate some key differences between the two operating systems.
Bypassing Return Flow Guard (RFG)
At the end of 2016, while checking for updates in Microsoft’s bounty program, I saw a reference to a new defense mechanism called “Return Flow Guard” (RFG). Since at that time I just finished the work on Liberation Guard, I took the time to check if can bypass this new protection method. This post will describe my attack on Microsoft’s Return Flow Guard, an attack that achieves full bypass of the protection method.
Liberation Guard – CFG Enhancement
In my search of Bug Bounty programs, I found Microsoft’s page and started to learn about CFG – Microsoft’s CFI implementation. From this research I developed “Liberation Guard”, a security enhancement to CFG that aims to block virtual table hijacking exploits.