Re: More info on MS99-061 (IIS escape character vulnerability)

From: Joakim Karlmark (joakim.karlmarkat_private)
Date: Sun Jan 02 2000 - 03:51:50 PST

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    > What does this allow you to bypass?  My guess is anything that plays or
    > needs the raw filename or request.  ISAPI filters and extension handlers
    > come to mind.  Who, what, where, and how are application specific.
    
    One category of systems that are vulnerable to this are
    3rd party authentications modules that do, for example radius
    authentication.
    
    One system that I've checked uses a special directory,
    lets call it /authRoot where the administrators can store
    customized login pages, graphics and so on.
    So, by neccessity, it allows unauthenticated access to this
    directory.
    
    Unfortunately the ISS bugg allows one to "break out" of this
    direcotry by appending %1u%1u  (".." in other words).
    So, to access default.asp we could would enter the url...
    
    http://server/authRoot/%1u%1u/default.asp
    
    And, ooops, unauthenticate access...
    



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