Re: The Dangers of Allowing Users to Post Images

From: Peter W (peterwat_private)
Date: Fri Jun 15 2001 - 13:33:25 PDT

  • Next message: Tim Nowaczyk: "Re: The Dangers of Allowing Users to Post Images"

    On Thu, Jun 14, 2001 at 09:12:05PM -0400, Chris Lambert wrote:
    
    > would it be safe to check
    > that if a referer is present, it contains the sites' domain name,
    
    Yes.
    
    > but if it
    > isn't, it most likely wouldn't have been referenced in an <img> tag or
    > submitted via JavaScript?
    
    You mean it's safe/legitimate? No. Client-pull META tags generate requests
    without Referers, as I've said a couple times in this thread, and in
    previous Bugtraq discussions, too. :-)
    
    If you don't see the Referer, you can't trust the request. Your best bet is 
    to lock out users who won't pass Referers.
    
    Or at least, when you initialize a user session, note if they seem to be
    passing Referer values. If they are, then you should certainly reject any
    later request that seems to be theirs, but lacks a Referer header.
    
    Note that in some cases, MSIE won't send a Referer if the TARGET of a link 
    is a different window, or that used to be the case. 
    
    This is messy.
    
    -Peter
    



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