Great Circle Associates Firewalls
(April 1995)
 

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Subject: Re: Secure Modem Pool
From: FV Admin mail <fvadmin @ sgf . fv . com>
Date: Tue, 25 Apr 1995 18:15:52 +0100
To: Ari Shamash <ari @ soscorp . com>
Cc: Steve England <se @ adv . sbc . sony . co . jp>, firewalls @ GreatCircle . COM
In-reply-to: <199504251416 . KAA02711 @ dauntless . soscorp . com>

> Generally, these kind of attacks work like this: a person trying to
> break in dials up the modem, and then simulates a hangup noise and
> dialtone WITHOUT ACTUALLY HANGING UP.  The dialback modem thinks the
> line has hung up, picks up the line, dials, and waits for a carrier.
> The person supplies a carrier, and viola, connects to the system.

Well, that's just *broken*.  Either that, or it's from the way-back days 
when the callee couldn't hang up on a call if the caller stayed off 
hook.  Nowadays, there's no possible reason why a callback modem wouldn't 
just hang up the line itself before picking up, listening for dial-tone, 
and dialing.

The other means of breaking into a callback modem is to have the phone 
company add call forwarding to the employee's phone (who checks?), have it 
forwarded to the cracker's modem, and then call in.  --Darren



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