DANGER, DANGER, DANGER
The WEB has gone crazy. I know that this is not news for some of you but you will be surprised to what extend this craziness has just developed. Among the traditional QuickTime Movie, QTL, Flash, Image, HTML and PDF vulnerabilities, there is now another one trivially exploitable with somewhat high degree of impact.
So we have changed a lot of diapers last year. Simple things we do suddenly have become very dangerous and risky. If you think that user supplied Image files are safe, think again. There were several attacks affecting social networks and a couple of very successful AJAX worms, again affecting social networks, during the last year. However, it seams that we haven't really scratch the surface yet.
You must understand that the attacker doesn't need to have write access to the specified PDF document. In order to get an XSS vector working you need to have a PDF file hosted on the target and that's all about it. The rest is just a matter of your abilities and desires.
This finding was originally mentioned by Sven Vetsch, on his blog. The attack vector was discovered by Stefano Di Paola and Giorgio Fedon. This is a very good and quite interesting finding. Good work.
Just to show you the impact of this issue I prepared the following POC.
When you open the PDF document, an XMLHttpRequest will be made to google.com and the front page source code will be displayed inside an alert box. Obviously, attackers can create a lot more dangerous scenario, where highly sensitive information is leaked leaving the user totally blind of what is going on.
This attack vector has several benefits that I must elaborate on. First of all, it is obvious that this is not a server side problem. This is totally client side and Web app owners cannot do much about it. The only solution is to have Adobe release a patch as soon as possible or just not to host PDF files at all. Obviously the second solution is highly unfeasible. This leave us with Adobe fixing the bug, but let's be honest with each other. Things won't get better. It is not that Adobe don't have good guys there or they are irresponsible. It is just the fact that not that many people update their PDF reader mainly because it usually requires a large chunk of data being downloaded and installed. The process is very slow and bulky and puts off even security-minded people.
Now we have a prove that every site on this planet is vulnerable to XSS (Cross-site scripting). This is definitely not nice. Unwillingly we have become solicitors of a very dangerous craft.