Recently we reported that the reason behind the Tumblr reblog attack is Stored cross Site scripting(XSS) vulnerability. The vulnerability was discovered by a security researcher Janne Ahlberg. Janne says the vulnerability is not yet fixed.
The vulnerability can be used for launching phishing attacks. For instance,it would be quite easy to ask input from user in various ways. User input could be stored to attackers server. Attacker could push malicious files from his/her server to Tumblr users.
"Attacker could create several Tumblr accounts and start blogging viral or popular videos using well chosen tags. Trust and popularity could be increased by using other accounts for reblogging video posts."Researcher described one possible attack scenario.
"Once the 'attack blog' would have enough followers, attacker could create a malicious post again with carefully selected tags. If the followers would reblog a malicious post, the spreading of payload would start."