An Analysis of CVE-2017-5638
I wrote a technical deep dive on CVE-2017-5638, which can be read here:
At GDS, we’ve had a busy few weeks helping our clients manage the risk associated with CVE-2017-5638 (S2-045), a recently published Apache Struts server-side template injection vulnerability. As we began this work, I found myself curious about the conditions that lead to this vulnerability in the Struts library code. We often hear about the exploitation of these types of vulnerabilities, but less about the vulnerable code that leads to them. This post is the culmination of research I have done into this very topic. What I present here is a detailed code analysis of the vulnerability, as well as payloads seen in the wild and a discussion on why some work while others don’t. I also present a working payload for S2-046, an alternate exploit vector that is capable of bypassing web application firewall rules that only examine request content types. I conclude with a couple of takeaways I had from this research.