Georgi Guninski security advisory #11, 2000 Hotmail security hole - injecting JavaScript in IE using "@import url(http://host/hostile.css)" Disclaimer: The opinions expressed in this advisory and program are my own and not of any company. The usual standard disclaimer applies, especially the fact that Georgi Guninski is not liable for any damages caused by direct or indirect use of the information or functionality provided by this program. Georgi Guninski, bears NO responsibility for content or misuse of this program or any derivatives thereof. Description: Hotmail allows executing JavaScript code in email messages using "@import url(http://host/hostile.css)", which may compromise user's Hotmail mailbox when viewed with Internet Explorer. Details: Several months ago in my Advisory #3, 2000 I alerted about a Hotmail bug with "@import url(javascript:...)". It was fixed, but now I found a similar bug. There is a new security flaw in Hotmail which allows injecting and executing JavaScript code in an email message using the the <STYLE> tag, @import and the "javascript:" protocol. This exploit works on Internet Explorer. Hotmail tries to filter JavaScript code for security reasons. Executing JavaScript when the user opens Hotmail email message allows for example displaying a fake login screen where the user enters his password which is then stolen. I don't want to make a scary demonstration, but it is also possible to read user's messages, to send messages from user's name and doing other mischief. It is also possible to get the cookie from Hotmail, which is dangerous. Hotmail deliberately escapes all JavaScript (it can escape) to prevent such attacks, but obviously there are holes. The following JavaScript is executed if embedded in a HTML message: ------------------------------------------- <STYLE type=text/css> @import url(http://www.nat.bg/~joro/test.css); </STYLE> ------------------------------------------- where http://www.nat.bg/~joro/test.css contains: ------------------------------------------- @import url(javascript:alert('JavaScript is executed')); @import url(javascript:eval(String.fromCharCode(97,108,101,114,116,40,39,84,101,115,116,32,49,39,41,59,97,108,101,114,116,40,39,84,101,115,116,32,50,39,41,59))); ------------------------------------------- Workaround: Disable Active Scripting before viewing a Hotmail message or don't use IE NOTE: Do not ask me to crack Hotmail accounts, I do not do that. Copyright 2000 Georgi Guninski Regards, Georgi Guninski http://www.nat.bg/~joro
