tumblr resolved issue of the viral post attack

tumblr was suffering from persistence xss as reported , now tumblr twitted that they resolved that issue

Tumblr engineers have resolved the issue of the viral post attack that affected a few thousand Tumblr blogs. Thanks for your patience.
— Tumblr (@tumblr) December 3, 2012

previously tumblr twitted about problem

We are aware that there is a viral post circulating on Tumblr. We are working to resolve the issue as swiftly as possible.Thank you.
— Tumblr (@tumblr) December 3, 2012

according to post on guardian.co.uk  : 

A group called the Gay Nigger Association of America, which says it is engaged in an "anti-blogging" campaign, took responsibility for the attack on Monday. The cyber worm infected major Tumblr accounts including those of USA Today, The Verge and Entertainment Weekly.