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6.3. Web Content Filtering
6.3.1. Overview
Web traffic is one of the biggest sources for security issues and misuse of the Internet.
Inappropriate surfing habits can expose a network to many security threats as well as legal and
regulatory liabilities. Productivity and Internet bandwidth can also be impaired.
Filtering Mechanisms
Through the HTTP ALG, NetDefendOS provides the following mechanisms for filtering out web
content that is deemed inappropriate for an organization or group of users:
•
Active Content Handling can be used to remove content from web pages that the
administrator considers a potential threat, such as ActiveX objects and Java Applets.
•
Static Content Filtering provides a means for manually classifying web sites as "good" or "bad".
This is also known as URL blacklisting and whitelisting.
•
Dynamic Content Filtering is a powerful feature that enables the administrator to allow or
block access to web sites depending on the category they have been classified into by an
automatic classification service. Dynamic content filtering requires a minimum of
administration effort and has very high accuracy.
Enabling Using IP Rules or IP Policies
Web content filtering scanning can be enabled using either an IP Rule object or an IP Policy
object.
With an IP Rule object, Web content filtering is first enabled on an HTTP ALG object. Then, that
ALG is associated with a Service object which is in turn is associated with an IP rule. The setup
example in this section uses an IP Rule object.
Configuring web content filtering using an IP Policy object is simpler than with an IP Rule object
since it is not necessary to configure separate ALG and service objects. However, certain ALG
options are not available with this method. Such an unavailable option is the Fail Mode
property, which is always set to Deny when using web content filtering with an IP Policy object.
The HTTP ALG is described further in Section 6.2.2, "The HTTP ALG" and IP Policy objects are
discussed further in Section 3.6.7, "IP Policy".
6.3.2. Active Content Handling
Some web content can contain malicious code designed to harm the workstation or the network
from where the user is surfing. Typically, such code is embedded into various types of objects or
files which are embedded into web pages.
NetDefendOS includes support for removing the following types of objects from web page
content:
•
ActiveX objects (including Flash)
•
Java applets
•
Javascript/VBScript code
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Chapter 6: Security Mechanisms
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