Nice find :) The problem does not rely on similarly named methods, rather it relies on the trust access checks that IE performs on function calls in disparate windows. When you try to alert each of the assign methods in your example their core toString methods are called which return a static string, however this is not used for comparison as each assign method still has their own unique internal ID. Instead, IE tries to determine whether the function call is safe based on the level of trust it has to the object that the method resides on. Your approach enables a range of method caching vulnerabilities by circumventing the object security check. This can be demonstrated by creating a cached reference to the location.assign method from the first window on the second windows location object, not just on the location.assign method but also on the location.replace method and the non-existant location.whatever property. I have added such a demo at http://www.pivx.com/research/2004/7/PaulsimilarMethodNameRedirection/tes t2.html Regards Thor Larholm Senior Security Researcher PivX Solutions 23 Corporate Plaza #280 Newport Beach, CA 92660 http://www.pivx.com thor@xxxxxxxx Stock symbol: (PIVX.OB) Phone: +1 (949) 231-8496 PGP: 0x4207AEE9 B5AB D1A4 D4FD 5731 89D6 20CD 5BDB 3D99 4207 AEE9 PivX defines a new genre in Desktop Security: Proactive Threat Mitigation. <http://www.pivx.com/qwikfix> -----Original Message----- From: Paul [mailto:paul@xxxxxxxxxxxxxxxx] Sent: Sunday, July 11, 2004 8:34 AM To: bugtraq@xxxxxxxxxxxxxxxxx Subject: MSIE Similar Method Name Redirection Cross Site/Zone Scripting Vulnerability Note: This vulnerability and many more can be found at http://www.greyhats.cjb.net SimliarMethodNameRedir Automatic Remote Compromise [Tested] IEXPLORE.EXE file version 6.0.2800.1106 MSHTML.DLL file version 6.00.2800.1400 Microsoft Windows XP sp2 [Discussion] At first I thought this vulnerability had something to do with method caching. It doesn't. It has to do with the security check that internet explorer has in place. Apparently, if a function is redirected to a function with the same name, it can be called without security restrictions. If you want to see what I mean, try this: <script> var var1=location.assign; alert("Assign function of the current window:\n"+var1); var w=window.open("about:blank","_blank"); var var2=w.location.assign; var w=alert("Assign function of the new window:\n"+var2); w.close(); </script> You should get two alerts describing the assign() function as being function assign(){ [Native code] } Notice both functions appear to be the same. My guess is that Internet Explorer checks the two function names and (maybe) the function code. If it matches, Internet Explorer marks the function as safe. It doesn't, however, take into account cross-window function calls. That's why SimilarMethodNameRedir works. How bad is this problem? Critical. With minimal effort, a malicious website owner could install viruses or spyware on the visitor's computer. Because theoretically this should work with every function, the only way that I can think of to fix the problem is to rewrite the whole function security check that internet explorer has in place. The best way to prevent this vulnerability is to either disable active scripting or switch to a different browser ;). The example goes to google.com and executes javascript that displays a messagebox with the location.href and the document.cookie attributes of the window object. [Example] http://freehost07.websamba.com/greyhats/similarmethodnameredir.htm
