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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.
stick to IE6. Long live Internet Explorer 6!
As usually they have a disclaimer too:
*This posting is provided "AS IS" with no warranties, and confers no rights*
If builders built buildings the way programmers wrote programs, then the first woodpecker would destroy civilization.
You mean like right clicking and selecting "not junk" ?
-]Phreak Out[-
Nah, it's more like this:
$ make meal ./meal
[tons of compiler output]
$
Segmentation Fault. Core dumped.
Colorless green Cthulhu waits dreaming furiously.
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.
The last sentence of the article's summary is completely wrong. I am one of the "original researchers" for this issue (p42.us is my website). The patches that have been issued by Microsoft up to this point are successful at eliminating the primary security vulnerability, to the best of our knowledge. The main security vulnerability described in our white paper was disclosed to Microsoft last fall and Microsoft fixed the issue in January 2010. The one case that has not been addressed by the filters is very rare and extremely unlikely to be found on a given websites.