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.
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.
Last post we discussed format string implementation vulnerabilities, and focused on the vulnerabilities in the (C/M)Ruby implementation. Since shopify integrated MRuby in a VM-like scenario, we will present a step-by-step exploitation of the main shown vulnerability, achieving a VM escape.
Format string vulnerabilities belong to a special family of vulnerabilities: a family of vulnerabilities that were once destructive but now days receive a decreasing amount of attention. Since most vulnerable code samples are based on poor C/C++ programming education, much like SQL Injections in SQL, most researchers believe that this vulnerability group can be completely mitigated with proper coding standards. However, this blog post will address a hidden aspect of the format string vulnerability, one that can impact quite a large number of high level programming languages.
The Integer-Overflow (IOF) vulnerability family is responsible for a dominant part of C/C++ code vulnerabilities, as I shown in my previous post with a specific example. However, the Integer vulnerability class has more than IOFs in it, and this will be the topic of this post.
After a long patching process, CVE 2016-8636 was now fixed and can be publicly disclosed. CVE 2016-8636 is caused by a classic integer-overflow vulnerability, showing that even the linux kernel suffers from this major vulnerability family.
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.