SummaryMinus ( http://min.us - now moved to http://minus.com ) is a simple sharing platform that allows users to share, publish and discover photos, docs, music, videos and more. This relatively new site has gained media attention and was recently featured in Techcrunch.com, Sitepoint, Lifehacker, Wall Street Journal etc. Minus recently raised $1M from IDG Capital Partners.
A few months ago I've found a way to silently upload and publish a file of attacker's choosing on behalf of a logged in Minus user, similar to what I found on Flickr. Today I present the vulnerability details with demonstration of an attack. The demo was first publicly disclosed at SecurityByte 2011.
The exploit is another example of HTML5 arbitrary file upload vulnerability, this time though it requires user interaction as the exploit uses UI redressing content extraction. The exploit is Firefox only.