Here's an old XSS exploit for Roundcube from 2013:
https://www.intelligentexploit.com/view-details.html?id=1696...
I still use RC despite the long history of XSS attacks against it. Luckily RC uses progressive enhancement, so it still works with JS turned off. I just assume emails can still execute JS in 2016? Perhaps it's wrong of me to use RC with JS turned off as a preventative measure, but you have to adore that user interface! It's the only reason I choose RC over other self-hosted email web apps (and there are few to choose from in this space). I like the simplicity of Squirrel-mail, but Roundcube looks and feels too good not to use.