I recently came across across a request on a bounty program that took user input and generated an image for you to download. After a little bit of a journey, I was able to escalate from XSS inside of an image all the way to arbitrary local-file read on the server. It's a private program, so I'm going to do my best to redact as much information as possible.
We recently started participating in Airbnb's bounty program on HackerOne. We heard a lot about this company in the past but had never used their service before. Overall they have a pretty solid website, but we were still able to discover a handful of issues. There is one vulnerability that we wanted to write about because of the level of protection in front of it. The goal of this write-up is to show others that sometimes it takes a little bit of creativity to discover potential flaws and fully exploit them.
The vulnerability we discovered is a series of Cross-Site Scripting attacks that involved bypassing JSON encoding, an XSS filter, a pretty decent WAF, CSP rules, and eventually getting it to bypass Chrome's XSS auditor.
In 2014 I discovered a vulnerability on Yahoo's Login Protection seal that allowed for CSS injection. This information was saved to the browser and IP, persisting across login sessions on that computer. The protection seal feature has since been removed from the login page, but the feature still exists in your account preferences.
The Facebook badges page was vulnerable to stored Cross-Site Scripting (XSS). This was initially reported back in August 2013, but due to communication problems over e-mail it wasn't fixed until early January. Neither party is to blame, but this shows some of the difficulties that companies can face communicating with security researchers.