Unclear what's happening but apparently imgur's looking into it - <a href="https://twitter.com/imgur/status/646109824342593536" rel="nofollow">https://twitter.com/imgur/status/646109824342593536</a>
Vulnerability has been patched. Details: <a href="https://imgur.com/blog/2015/09/22/imgur-vulnerability-patched/" rel="nofollow">https://imgur.com/blog/2015/09/22/imgur-vulnerability-patche...</a>
Interesting they would choose 8chan. But then again, maybe it's a test run? Take a semi-popular site then when it works there (assuming the discovery wasn't made) then try something bigger like Facebook?