Exploit Archeology - Exploiting an old unknown Server Side Browser

I was recently hacking on a Bug Bounty target and identified an interesting API endpoint which would render user supplied HTML, and execute any included JavaScript. Exploiting Server Side Browser bugs has been a focus of mine for the past couple of years, so I set out to exploit this newly identified feature. This blog post details my journey into researching and exploiting what turned out to be a decade old Server Side Browser.