Re: A technique to mitigate cookie-stealing XSS attacks

From: Justin King (justinat_private)
Date: Thu Nov 07 2002 - 12:26:49 PST

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    I would be very interested in major browsers supporting a <dead> tag with an
    optional parameter to be a hash of the data between the opening and closing
    dead tag. This tag would indicate that no "live" elements of HTML be
    supported (e.g., JavaScript, VBScript, embed, object).
    
    I know this has been suggested before. I would prefer to see RFC covering
    this, with support an implementation immediately following.
    
    -Justin
    
    ----- Original Message -----
    From: "Michael Howard" <mikehowat_private>
    To: <bugtraqat_private>
    Sent: Tuesday, November 05, 2002 13:44
    Subject: A technique to mitigate cookie-stealing XSS attacks
    
    
    During the Windows Security Push in Feb/Mar 2002, the Microsoft Internet
    Explorer team devised a method to reduce the risk of cookie-stealing
    attacks via XSS vulnerabilities.
    
    In a nutshell, if Internet Explorer 6.0 SP1 detects a cookie that has a
    trailing HttpOnly (case insensitive) it will return an empty string to
    the browser when accessed from script, such as by using document.cookie.
    
    
    Obviously, the server must add this option to all outgoing cookies.
    
    Note, this does _not fix_ XSS bugs in server code; it only helps reduce
    the potential damage from cookie disclosure threats. Nothing more. Think
    of it as a very small insurance policy!
    
    A full write-up outlining the HttpOnly flag, as well as source code to
    set this option, is at
    http://msdn.microsoft.com/library/en-us/dncode/html/secure10102002.asp.
    
    Cheers, Michael Howard
    Secure Windows Initiative
    Microsoft Corp.
    
    Writing Secure Code
    http://www.microsoft.com/mspress/books/5612.asp
    



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