Re: The Dangers of Allowing Users to Post Images

From: Brett Lymn (blymnat_private)
Date: Sun Jun 17 2001 - 05:40:18 PDT

  • Next message: Peter W: "[Fwd: Re: Cross-Site Request Forgeries (Re: The Dangers of Allowing Users to Post Images)]"

    According to Tim Nowaczyk:
    >
    >  My company implemented this but went one more step.  They created a
    >  file that had (IP, ticket) pairs. The ticket was passed around in
    >  URLs, but wasn't valid unless it came from the specific IP.  To
    >  pretend to be someone else, one would have to spoof their IP and
    >  guess the value of their (10 hour life-cycle) ticket.  We did this,
    >  originally, because we wanted to support web browsers that didn't
    >  use cookies.  The file was, actually, more like (IP, ticket,
    >  cookie-type-options-and-settings).  It worked well for us.
    >
    
    You are lucky.  There are two cases which will invalidate this
    solution:
    
    1) A bunch of users are behind a single web proxy (such as squid) so
       they all appear to come from the same IP address.  This means you
       will have multiple tickets for the same IP.
    
    2) A bunch of users are behind a multi-parented web proxy, in which
       case the users will appear to come from one of a number of
       addresses.  This leads to bizarre behaviour - the user
       authenticates successfully but gets kicked off later because the
       ticket/IP pair don't match because a different parent to the one
       the user authenticated on happened to handle the request.
    
    -- 
    ===============================================================================
    Brett Lymn, Computer Systems Administrator, BAE SYSTEMS
    ===============================================================================
    



    This archive was generated by hypermail 2b30 : Mon Jun 18 2001 - 23:13:12 PDT