Sure they are , if you do not user Firefox (even the last version) or if you do not use iOs 6.1 or some older version of IE they are really safe :) In the last few days I got the pleasure to be in touch with the github security guys . I must admit I am really impressed about how security is important for Github and how much serious they take it (they embrace and leverage all the new security features supported by modern browsers, Content Security Policy included ). Moreover they are really fast on reply and really friendly so kudos to them. From the other hand I was a bit surprised on how the "handled" a couple of issues I did report. Now the fact I did not get a bounty doesn't play any role on my opinion (apparently both issues I reported were well known by them). The thing that does surprise me instead is the fact that even that those are well known issues are not yet fixed (if ever). But no more words just fact... The first issue I reported is the following.