Gregory Maxwell wrote:
Please no scare mongering. Wikimedia sites are not vulnerable to this.
I reproduced the vulnerability the day it hit Slashdot and determined that it posed no special risk to us.
[...]
The reason that Wikimedia sites are not vulnerable is that wikimedia sites confine all user uploaded files to upload.wikimedia.org which holds nothing but these files. XSS attacks via uploaded files (which is what this effectively is, though it's using Java) end up confined by browser behaviour to only access that particular domain (or IP, in the case of Java). Since there is nothing worth targeting on that IP (no login, no cookies, no forms, etc) it couldn't do much.
All the same, I'd rather not have such files on our servers. I'm glad someone finally reported this, and it would have been nice if you filed a bug at the time.
Even if Wikimedia is not vulnerable, many other MediaWiki installations will be.
-- Tim Starling