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Re: tcp,guardent,bellovin

  • From: Jim Duncan
  • Date: Mon Mar 12 22:39:45 2001

Rafi Sadowsky writes:
>  No eavesdropping at all ? how can a TCP connection be hijacked if you're
> not on the connection path?
> (Or capable of diverting the connection past you -
>  breaking routers/source_routing/<whatever>.... )

The attacker merely has to get his data into the TCP stream on the 
victim host.  No return traffic necessary.  This means the attacker can 
be _outside_ the victim's network if source address forgery isn't 
prevented.  This is _not_ new; same attack Mitnick used on Shimomura.

If you're on the path, you certainly don't need to guess the TCP ISN to 
hijack a connection.  This isn't new, either. :-)

By the way, Cisco stuff that has the fix we advertised in the security
advisory a couple of weeks ago is *NOT* vulnerable to the attack
announced by Guardent.  The older stuff in IOS is not vulnerable either,
but some of our other products _are_ vulnerable.  Of course, we already
announced that at .

I'll be along with a more official announcement, but I figured I'd
mention it here, too.


Jim Duncan, Product Security Incident Manager, Cisco Systems, Inc.
E-mail: <>  Phone(Direct/FAX): +1 919 392 6209

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