FortiOS 6 – Web Filtering

Web filter

This section describes FortiGate web filtering for HTTP traffic. The three main parts of the web filtering function, the Web Content Filter, the URL Filter, and the FortiGuard Web Filtering Service interact with each other to provide maximum control over what users on your network can view as well as protection to your network from many Internet content threats. Web Content Filter blocks web pages containing words or patterns that you specify. URL filtering uses URLs and URL patterns to block or exempt web pages from specific sources. FortiGuard Web Filtering provides many additional categories you can use to filter web traffic.

This Handbook chapter includes Inside FortiOS: Web Filtering and provides readers an overview of the features and benefits of key FortiOS 5.6 components.

For further detail than the Inside FortiOS document, we provide the following topics:

Web filter concepts

Inspection modes

FortiGuard Web Filtering Service

Configuring web filter profiles

Overriding FortiGuard website categorization

Using cookies to authenticate users in a Web Filter override

Web Profile Overrides


YouTube Education Filter

Static URL filter

Web content filter

Web filtering example

Advanced web filter configurations

Web filter concepts

Web filtering is a means of controlling the content that an Internet user is able to view. With the popularity of web applications, the need to monitor and control web access is becoming a key component of secure content management systems that employ antivirus, web filtering, and messaging security. Important reasons for controlling web content include:

  • lost productivity because employees are accessing the web for non-business reasons l network congestion — when valuable bandwidth is used for non-business purposes, legitimate business applications suffer
  • loss or exposure of confidential information through chat sites, non-approved email systems, instant messaging, and peer-to-peer file sharing
  • increased exposure to web-based threats as employees surf non-business-related web sites l legal liability when employees access/download inappropriate and offensive material l copyright infringement caused by employees downloading and/or distributing copyrighted material.

Web filter concepts

As the number and severity of threats increase on the World Wide Web, the risk potential increases within a company’s network as well. Casual non-business related web surfing has caused many businesses countless hours of legal litigation as hostile environments have been created by employees who download and view offensive content. Web-based attacks and threats are also becoming increasingly sophisticated. Threats and web-based applications that cause additional problems for corporations include:

  • spyware/grayware l phishing l pharming l instant messaging l peer-to-peer file sharing l streaming media l blended network attacks.

Spyware, also known as grayware, is a type of computer program that attaches itself to a user’s operating system. It does this without the user’s consent or knowledge. It usually ends up on a computer because of something the user does such as clicking on a button in a pop-up window. Spyware can track the user’s Internet usage, cause unwanted pop-up windows, and even direct the user to a host web site. For further information, visit the FortiGuard Center.

Some of the most common types of grayware infection occur when:

  • downloading shareware, freeware, or other forms of file-sharing services l clicking on pop-up advertising l visiting legitimate web sites infected with grayware.

Phishing is the term used to describe attacks that use web technology to trick users into revealing personal or financial information. Phishing attacks use web sites and email that claim to be from legitimate financial institutions to trick the viewer into believing that they are legitimate. Although phishing is initiated by spam email, getting the user to access the attacker’s web site is always the next step.

Pharming is a next generation threat that is designed to identify and extract financial, and other key pieces of information for identity theft. Pharming is much more dangerous than phishing because it is designed to be completely hidden from the end user. Unlike phishing attacks that send out spam email requiring the user to click to a fraudulent URL, pharming attacks require no action from the user outside of their regular web surfing activities. Pharming attacks succeed by redirecting users from legitimate web sites to similar fraudulent web sites that have been created to look and feel like the authentic web site.

Instant messaging presents a number of problems. Instant messaging can be used to infect computers with spyware and viruses. Phishing attacks can be made using instant messaging. There is also a danger that employees may use instant messaging to release sensitive information to an outsider.

Peer-to-peer (P2P) networks are used for file sharing. Such files may contain viruses. Peer-to-peer applications take up valuable network resources and may lower employee productivity but also have legal implications with the downloading of copyrighted or sensitive company material.

Streaming media is a method of delivering multimedia, usually in the form of audio or video to Internet users. Viewing streaming media impacts legitimate business by using valuable bandwidth.

Blended network threats are rising and the sophistication of network threats is increasing with each new attack. Attackers learn from each successful attack and enhance and update their attack code to become more dangerous and to spread faster. Blended attacks use a combination of methods to spread and cause damage. Using virus or network worm techniques combined with known system vulnerabilities, blended threats can quickly Web filter concepts

spread through email, web sites, and Trojan applications. Examples of blended threats include Nimda, Code Red, Slammer, and Blaster. Blended attacks can be designed to perform different types of attacks, which include disrupting network services, destroying or stealing information, and installing stealthy backdoor applications to grant remote access.

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