IT Baseline Protection Manual - The Information Warfare Site

Safeguard Catalogue - Communications Remarks
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gateway, because in these circumstances active content can no longer cause
any harm in the internal network.
Another solution is to allow only certain WWW browsers to be used for
access to the Internet. Netscape Communicator and Internet Explorer are not
the only browsers available; there are also other browsers that have no means
of executing active content.
One option is to ensure that browsers of this type will be used by setting up
the administration of the workstations to this effect. In this case, however, the
operating systems of the workstation must provide reliable separation of roles
between users and administrators, such that configurations set by the
administrator cannot be revoked by a user. Additional security precautions are
therefore necessary with operating systems such as Windows 3.1 and
Windows 95.
Alternatively, the proxy on the firewall could be set up in such a way that only
predefined browser software is allowed access to the Internet. It must be borne
in mind in this case, however, that the security of this method is dependent on
the ID of the WWW browser used. A skilled user with a hex editor should
have no difficulty modifying a WWW browser of his choice in such a way
that it has the desired ID.
Raising the awareness of users
It is also conceivable to place the responsibility entirely in the hands of the
users. Active content should normally be deactivated in the WWW browser,
but the users have permission to run active content in certain circumstances.
This could be the case for example if they were no longer able to access the
WWW information provided by a well-known manufacturer without running
the active content.
ActiveX, in particular, has various security settings, which enable the
execution of ActiveX to be restricted to certain WWW servers so that users
are not forced to change their settings repeatedly.
There must be some doubt, however, whether users will really always change
the security settings of their WWW browsers when they switch to another
WWW page, for example where a link from the "well-known manufacturer"
may have taken them. Besides, an individual Web page on a "secure"
computer can also load other Web pages which are located on "non-secure"
computers. As well as that, attacks can be made on the Internet which have the
effect that users do not receive the WWW page that they requested (see T 5.48
IP spoofing and T 5.78 DNS spoofing, for example).
Filtering specific active content
Recently programs have been developed which work in a similar way to
computer virus scanning programs by examining active content to determine
whether it contains code that is a threat to security. This is a highly acceptable
solution for users, because they can then access all harmless active content.
The question has to be asked, though, whether such programs really provide
protection. A virus scanning program cannot provide protection against Trojan
horses, for example, and these can of course cause considerable damage.
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IT-Baseline Protection Manual: Oktober 2000