Hello, I noticed an XSS on imgur. Proof of concept: visit the URL
It's not the simplest case as it requires some React magic. There is a good explanation of this type of vulnerabilities at http://danlec.com/blog/xss-via-a-spoofed-react-element . Corresponding H1 report: https://hackerone.com/reports/49652 .
The impact is as usual. The attacker could execute operations on behalf of the victim who visits a malicious link, or access e.g. the session cookie (IMGURSESSION).
I haven't yet checked if this the only such occurrence on Imgur.