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IE8's XSS Filter Exposes Sites To XSS Attacks
Blue Taxes writes "The cross-site scripting filter that ships with Microsoft's Internet Explorer 8 browser can be abused by attackers to launch cross-site scripting attacks on websites and web pages that would otherwise be immune to this threat. The IE8 filter works by scanning outbound requests for strings that may be malicious. When such a string is detected, IE8 will dynamically generate a regular expression matching the outbound string. The browser then looks for the same pattern in responses from the server. If a match is made anywhere in the server's response, the browser assumes that a reflected XSS attack is being conducted and the browser will automatically alter the response so that the XSS attack cannot succeed. The researchers figured out a way to use IE8's altered response to conduct simple abuses and universal cross-site scripting attacks, which worked against sites that would not otherwise have been vulnerable to XSS." Here is the researchers' backgrounder (PDF) on the attack. Microsoft says that they have issued two patches that address the issue, but the researchers insist that holes remain.
Update: 04/20 14:06 GMT by KD : Microsoft's Security Response Center has issued a statement on the vulnerability.
Update: 04/20 14:06 GMT by KD : Microsoft's Security Response Center has issued a statement on the vulnerability.
http://blogs.technet.com/msrc/archive/2010/04/19/guidance-on-internet-explorer-xss-filter.aspx
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stick to IE6. Long live Internet Explorer 6!
Close, but no cigar.
Really, if you want a first post, subscribe to the site. You will get your silly kicks, and the rest of us will at least know you are making a valuable contribution to the site by paying the rest of the users to be silly.
Moved to http://soylentnews.org/. You are invited to join us too!
You mean like right clicking and selecting "not junk" ?
-]Phreak Out[-
You hired a guard and he raped your daughter. Now your neighbor also has a daughter and he hired another guard. Somehow, that guard decided to emulate the broken behavior of your guard as well.
Would that not simply mean that those who were born daughters were simply inviting rapists as opposed to rapists somehow being responsible?
If you can't understand the above analogy, here's a Car Analogy for you.
You drove a Toyota on the road and killed a pedestrian due to negligence. Someone else driving a Ford emulated your broken behavior and killed another pedestrian. It means that the pedestrians were simply choosing the insecure way of transportation as opposed to drivers somehow being responsible.
Colorless green Cthulhu waits dreaming furiously.
will dynamically generate a regular expression matching the outbound string
RegEx? Dynamic? Generated?? I don’t think I’m the only one who got the chills and raising hackles from this...
I think this deserves an award for the most made-for-disaster concept even conceived. ^^
Any sufficiently advanced intelligence is indistinguishable from stupidity.
I'm sure your user will be deeply affected by this.
Honestly, I usually am the first to lay the blame on developers for doing half-arsed jobs, but in this case... really, why would I blame a site for a modification a third party plugin does to their HTML code? As per the specs, their code is secure. Then someone comes and changes it to something insecure. Why would you hold the former responsible for something done by the latter.
I mean, let's say you write some program, and check your array bounds and everything. Then a year later I'm brought in as a consultant and, perhaps in the name of optimizing speed, inadvertently bypass one of your checks and introduce a buffer overflow vulnerability. Would you say that you should be held responsible for my changes? Would you say your code was simply insecure if it allowed that? Why? By what definition of "insecure"?
Plus, I always believed that responsibility should also come with enough power to do what you're responsible for. E.g., if you're responsible that a project finishes on time, then you should also have the power and budget to make sure it does. Responsibility without any power is IMHO just a name for "scapegoat."
In this case, the IE code and its modifications are completely outside the web designer's control. If Microsoft introduces a new vulnerability next month, which turns a whole other chunk of perfectly good web programming into an XSS exploit vector, the web designer can't do anything to prevent them. It's exactly that scapegoat scenario. You're proposing to hold someone responsible for something they can't prevent or even influence at all.
Plus, it's not like MS's code is public domain or even has an open and detailed specification. You can work around Javascript or HTML problems because you can know exactly what they are, what that code does, what does it output for a given input, etc. (Well, that is, if the browsers actually implemented the specs;)) In this case to work around MS's bug du jour, someone has to keep basically reverse-engineering whatever idiocy MS implemented this time. It seems to me like an undue burden.
Plus, honestly, writing stuff that only works because of a bug in another module (in this case the browser) is bad practice. Now I'm aware that it can't always be avoided. But at least in an ideal world, it should be MS's job to fix MS's bugs, not the devs job to work around it. The devs job should be to write stuff that is correct and secure by the Javascript/HTML/whatever standards, not code that works with the IE bug of the day.
A polar bear is a cartesian bear after a coordinate transform.
No.
The sites were previously not susceptible to cross-site scripting. They escaped their input, whatever needed to be done.
IE cleverly tried to prevent cross-site scripting and in the process they screwed up the properly-escaped response so that now, you can execute a xss attack that didn’t even exist until IE8 changed it.
This is how.
If I enter “<img src=x:x onerror=alert(document.cookie);><script” in a username field, the next page that says “Hi, $name” should not result in a script alert. And if the page also sends the username as a Javascript string, the (PROPERLY ESCAPED) response might look like this:
<script type="text/javascript">
var username = "<img src=x:x onerror=alert(document.cookie);><script";
</script>
Hi, <img src=x:x onerror=alert(document.cookie);><script
Note that the site properly escaped the angle brackets when it was presented as HTML, and there were no illegal characters that needed escaping in Javascript.
IE8 will detect your “<script” in the input and replace all instances of <script with “<sc#ipt” in the resulting page. (No, I’m not making this up. That is what the researchers claim.) Which, naturally, kills most of the Javascript functionality in the resulting page. But more importantly, it does this:
<sc#ipt type="text/javascript">
var username = "<img src=x:x onerror=alert(document.cookie);><sc#ipt";
</script>
Hi, <img src=x:x onerror=alert(document.cookie);><script
...which looks like this, when the browser renders it:
var username = "[broken image bitmap] Hi, <img src=x:x onerror=alert(document.cookie);><script
AND THE INJECTED SCRIPT EXECUTES.
Now you just replace the alert() with some Ajax code to send the stolen cookies to your server, craft a URL containing the malicious code in a GET query, and go phishing.
Alexander Peter Kristopeit bought his basement from his mommy for one dollar.
When you go to a website, and it says "Welcome, Thomas!" because your referrer website sent them to their homepage with something like "http://www.website.com/?name=Thomas" these guys set up the referrer to send you to a page that says something like "http://www.website.com/?name=[malicious code]" and the site says "Welcome !" and congratulations on your new site-specific keylogger.
I am the richest astronaut ever to win the superbowl.