Tag Archives: security

Mozilla causing XSS in Livejournal

As mentioned in my last entry, Livejournal have changed their url scheme to get around a problem in mozilla. The trouble is down to the -moz-binding CSS property. I’ll repost a copy of the short lived posting to the lj_dev community earlier.

Discussing the URL Change

As we recently announced in

news, we have changed the canonical URL of most journal, community, and syndicated content. While we did offer subdomains to Paid users in the past, this is now the canonical URL that we will link and redirect to for all journals. However, all communities are located at http://community.livejournal.com/username and syndicated accounts at http://syndicated.livejournal.com/username. Due to the way certain proxy servers are configured, and the fact that the HTTP RFC prohibits it, the canonical URL for journals with a username starting with an underscore will be http://users.livejournal.com/username. We are however offering a free rename if you fall into this group.

So now the technical side of all of this and why it was a required change; bear with me as its 3am my time and I’m sitting in John F. Kennedy Airport after a five hour flight. Late last week we become aware that it was possible to use the “-moz-binding” CSS attribute within Mozilla and Mozilla Firefox to execute arbitrary offsite JavaScript. As this attribute is designed to allow attaching an XBL transform and JavaScript to any node within the DOM, it is quite easy to use in a malicious fashion. We immediately altered our cleaner to strip this attribute from entries and comments, though also realized that wasn’t even half the battle.

As we allow custom CSS in many of our styles, as well as the ability to link to an external stylesheet in a variety of fashions, it was quite possible to take advantage of this exploit and hijack the session cookie of any user who views your journal. As we, along with many other sites, used one cookie to authenticate a user, this cookie was quite powerful if stolen. If the user had not chosen to bind their cookie to their IP address, a malicious user could steal it, login as that user, deface the account and SPAM with it, as well as modify that user’s style to include the exploit thus causing this problem to spread much like a virus.

Borrowing the idea from another development team within Six Apart, we decided we needed to break our cookies into three categories. One cookie would be our application management cookie, this cookie would only be accessible on www.livejournal.com where we will not display untrusted content. A second cookie will be accessible on all subdomains of livejournal.com, though it only will say if you are logged in or not; it is solely for optimization. We then will issue one cookie for each journal you visit. This cookie will be only accessible on username.livejournal.com or community.livejournal.com/username as it is limited to a single journal. This cookie will only grant you the permission to read protected entries and post in the particular journal. This means that if the journal owner steals your cookie, they will be able to do nothing more than view their journal and comment upon it as if they are you. In the end you will have n+2 cookies, with n being the number of journals you visit.

Due to the fact that we cannot clean every external CSS stylesheet linked to every time we generate a journal page, this change is required. While it does not fully protect us from some new cross site scripting vulnerability that can be exploited via entries or comments, they are much easier to block, patch, and recover from quickly. With Mozilla deciding to allow the execution of arbitrary JavaScript via CSS, there is no other viable solution than the one we have undertaken. We developed a plan to phase all of this in over the next week, URL change first and then followed by the cookie change, though this morning we were made aware that this was being actively exploited. As such we took our week time line and shortened it to about twelve hours. While URLs have been changed at this time, our cookie handling change has not yet happened. This should however be expected to take place within the next day or two as well as various other cleanups and fixing bugs we’ve already encountered.

Please feel free to let us know if you have any questions and open a support request if you find a bug or encounter a problem. Sorry all of this came with just about zero warning, but in the end we could not wait longer to fix this problem.

Thanks to Daniel Silverstone for providing me with a cache copy of the text.

Unintended Consequences of Technology

I’ve been meaning to post this for a couple of days. I discovered a
rather unintended and quite unexpected consequence of using a piece of
software. At work I use Workrave to enforce
breaks from the computer. For those that have never used it, workrave is
a little gnome applet that monitors your keyboard and mouse usage and
after about an hour of work locks your screen and gives you a 10 minute
break with a few exercises to reduce RSI. It also gives you microbreaks
of 20 seconds every 3 minutes of work, so you can look away from the
screen, stretch, whatever.. I should point out that it isn’t 20 seconds
every 3 wallclock minutes, but 3 minutes of using the mouse/keyboard and
isn’t quite as intrusive as it sounds.

I get to rest my eyes, prevent RSI annd take breaks. This sounds like
exactly the thing Workrave was written for. So what is unintended? It
turns out that the 20 seconds micro-break is just the right amount of
time to have a drink of water or get up and fill my glass if it’s empty.
Before I would forget to fill my glass up, but now I have time where I
can’t do anything on the computer. In the 30 minutes since I got in to
the office and started writing this entry I’ve had two micro-breaks and
drunk a pint of water. Workrave has managed to increase my water intake
during the day and as a result the number of toilet breaks. 🙂

I notice LiveJournal have
enforced http://<username>.livejournal.com/ url scheme now to
prevent cross-site scripting attacks where people were stealling session
cookies and gaining access to accounts. Not sure what the exact problem
was, but I know of several attacks over the last week by one group of
scriptkiddies.

Update: Appears the problem was in firefox. Explaination
here.

Update: Nope, they pulled it. Basically mozilla allows you to execute
javascript via CSS stylesheets. I’ll update with any further URLs as
they become available.

The dangers of relying on others

I use bitlbee for talking on MSN
and other IM protocols. It is a irc to IM gateway so I can use my
normal irc client to talk to people that insist on using silly
protocols. (Predictably I use irssi) The reason I use bitlbee over
something like gaim that when I used to use gaim or kopete I found
that having a second window to check for activity meant that I would
either ignore stuff on irc or on msn while talking on the other.
Using bitlbee fixed this problem as an MSN chat just appeared as
another privmsg. Plus I could use the same logging system for both.

For the last few months I’ve been using a public bitlbee server at
im.bitlbee.org, which had been working perfetcly find until the tail
end of last week when it kept getting connection refused.
Suddenly on Saturday morning, that machine changed from running a
bitlbee server to running an ircd for the Net24 irc network. As
bitlbee works by joining you to your own private #bitlbee channel
where you talk to a bot to control the client, when a proper ircd
appeared, everyone using that server suddenly joined the global
#bitlbee and several people auto-authenticated to the channel,
revealing their passwords.

It’s times like this when I’m glad I never get round to doing things
like setting up auto-identifying to bitlbee.