Re: FW-1 DOS attack: PART II

From: Steve Birnbaum (sbirnat_private)
Date: Tue Aug 03 1999 - 20:22:02 PDT

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    lanceat_private said:
    >  I have not tested that yet, so I cannot confirm nor deny its
    > validity, however I have heard of this behavior before.  Looks like I
    > have a new challenge to play with :)
    
    I tested it some time ago under 3.0b (maybe with some patches added).  They
    might have changed it since then, of course.
    
    As someone else has already stated in this thread, when installing a policy
    the state table is reset.  So as not to have all existing connections dropped
    when this happens, Checkpoint had/have this "feature" that allows ACK packets
    in.  It is only supposed to allow ACK packets in that correspond to the
    reverse of an outgoing rule.  Therefore, if there is nothing allowed out,
    it's not supposed to allow the ACKs in.  If you allow all internal hosts to
    access the Internet on all ports, it'll allow in most packets.
    
    The body gets mangled, but I'm not sure about the sequence numbers.
    
    Depending on the response of the internal host the connection will be added
    to the state table.
    
      Steve
    
    --
    Steve Birnbaum  -  sbirnat_private      (PGP key available)
    
    
    
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