With this bug, a local attacker can infect users with malware. it works this way, after the sign up page or most pages, a Download prompt appears. (for example, at your Hackerone Page hackerone.com/owncloud), However, the downloads url, in my case, it was
Did you see what I see? the page is delievered by http. so an attacker does this, downloads the file, bind a malware to it. host it to his server, and when a legit user try to donwload it, deliever the payload binded with the games. user runs that, game over. who's to blame? well, duh... owncloud!
The easiest solution is just changing the URL from http://download.owncloud.org/community/owncloud-daily-stable8.1.tar.bz2 to https://download.owncloud.org/community/owncloud-daily-stable8.1.tar.bz2 because the site works both ways, only... the second one gets downloaded from an encrypted source. I don't even know why you put the HTTP version anyways.
Note: I am doing this for the points, not the bounty. so please don't damage it.
Thanks again, Paulos