D-Link DFL-2500 User Guide - Page 32

3.2. What does a Firewall NOT protect against? 13 • Customized scripts on web servers. It is now very easy to extend the functionality of your web server by writing small, customized programs to handle a multitude of tasks. However, insufficient awareness of potential problems can lead you, more often than not, to make small, difficult to detect mistakes that will enable an intruder to gain access to your system. • Web browsers. Automation of processes and simplifying operations for the benefit of users creates increased internal complexity and thereby increased risks of vulnerabilities. • Desktop software, primarily that which to great extent support scripting languages, for the same reason as browsers. Scripting languages provide almost unlimited access to local computers and all connected network resources. As a result, intruders can cause all types of problems if they can get internal users to open documents containing malevolent scripts. 3.2.4 Internal Attacks A firewall can only filter data that passes through it. Therefore it can't offer any protection from internal attacks on local networks, where all computers communicate directly with each other. In addition, firewalls cannot provide protection against local users introducing harmful software to the network from a removable media, or by exporting sensitive information in the same manner. This may seem obvious. However, most people underestimate the impact of such damage. Although different sources provide different figures, it is clear that more than 50% of all data security problems are the results of internal attacks. Some sources put this figure as high at 80%. 3.2.5 Modems and VPN Connection A common misconception is that modems and VPN gateways are as secure as the protected network and can be connected directly to it without protection. D-Link Firewalls User's Guide