IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Communications Remarks
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prompt involvement of the staff council or works council should be borne in
mind.
Reservations regarding the use of a fax server are often due to the fact that an
IT system which is integrated into the LAN can be accessed over the public
telecommunications network.
Through careful selection and configuration of communications cards,
operating system and fax server application and secure positioning of the
server in the network topology, the danger of penetration of the network or the
fax server can be reduced to a minimal residual risk.
Where active ISDN cards are in use, features which are not necessary for
receiving and sending faxes should be disabled (see S 4.59 Deactivation of
ISDN board functions which are not required).
Where dedicated fax cards are used, once again it is important to find out at
the outset exactly what facilities are provided, and, if possible, to disable any
unnecessary features which are not required.
The fax service should be the only service provided by the fax server. In
particular, a fax server should not be used also as a data, printer, e-mail or
Internet server or as a remote access computer. To reduce the probability of
penetration over the telecommunications network, the operating system must
be configured as "lean" as possible. This means that services and protocols
which are not really necessary for operations are not installed. For example, if
the Telnet service is not started up on a fax server, then it is not possible for an
attack to occur from this source. When deciding which services and protocols
are necessary, it should be borne in mind that dangers often arise from the
combination of different services and protocols.
How the server is securely positioned in the network topology depends partly
on whether any firewall is in use in the organisation and, if so, which type.
A fax server has a minimum of one interface to each of the
telecommunications network and the LAN. The fax server should be placed in
the network in such a way that in the event of a successful attack on the fax
server it is not possible for the adversary to penetrate the entire network. On
the other hand it must not be possible to attack the fax server successfully
from within the network either. For example, it is conceivable that an attack
could be launched by an adversary from the Internet. If such an attack
succeeds, the perpetrator is then in a position to arrange for faxes to be sent
out using the fax server of the attacked organisation. This not only results in
telephone charges but, even more serious, could harm the company's
reputation. If the attacker succeeds in getting through, he will also be able to
view the fax transmissions stored either permanently or temporarily on the fax
server, despite not being authorised to do so. Similarly, attacks by insiders
over the LAN are also feasible.
As a fax server usually is not the only IT component which is connected to an
external network, there will normally be a barrier to protect the internal
network against external networks (see also Section 7.3 Firewalls).
If there is a screened subnet acting as Internet firewall (configuration 1 from
S 2.73 Selecting a suitable firewall), the fax server should be positioned
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IT-Baseline Protection Manual: Oktober 2000
Deactivation of
unnecessary facilities
One service per server
Position of the fax server
in the network
Position of fax server
where there is a firewall