The risks of client systems writing to server registry

From: Richard Bartlett (richardat_private)
Date: Thu Sep 05 2002 - 06:47:39 PDT

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    All,
    
    I have a customer who is developing some printer driver code to allow 
    custom driver settings (n-up, booklet, duplex etc.) to be saved up to the 
    server to be retrieved by other users.   The data is being written, by a 
    printer driver (using the logged on users authentication, to a registry 
    key) HKLM\SYSTEM\CurrentControlSet\Control\Print\Environments\Windows NT 
    x86\Drivers\Version-3\{Driver Name}\{Custom Key}\Subkey).
    
    The question is, what are the security risks of allowing users to write 
    to this key?  The data is string data, in the form of delimited numeric 
    values.  This data is then retrieved by capable printer drivers and 
    interpreted.
    
    The risks as I see it are twofold;
    (1) The risks of a compromise to the server using this registry key.  I 
    think this is unlikeley as the server itself does not use this data, only 
    client PC's do.  Unless someone knows a way to travel out of a hive up 
    the registry bypassing the permissions set using regedt32.
    (2) The risks of a compromise to the client (far more likely).  This 
    would probably be by a malformed or extremely long string in the key 
    value, which would presumably lead to either DOS or system compromise by 
    buffer overflow on the client system.
    
    Does anyone else have any thoughts on this?
    
    Richard Bartlett
    Hacker Immunity Ltd
    



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