Securing Your Web Browser PART I
"This paper will help you configure your web browser for safer internet surfing. It is written for home computer users, students, small business workers, and any other person who works with limited Information Technology (IT) support and broadband (cable modem, DSL) or dial-up connectivity. Although the information in this document may be applicable to users with formal IT support as well, organizational IT policies should supersede these recommendations. If you are responsible for IT policies for your organization, please consider implementing these recommendations as part of your policy."
Introduction
Introduction
- Why Secure Your Web Browser?
- Web Browser Features and Risks
- How to Secure Your Web Browser
- Keeping Your Computer Secure
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I. Why Secure Your Web Browser?
Today, web browsers such as Internet Explorer, Mozilla Firefox, and Apple Safari (to name a few), are installed on almost all computers. Because web browsers are used so frequently, it is vital to configure them securely. Often, the web browser that comes with an operating system is not set up in a secure default configuration. Not securing your web browser can lead quickly to a variety of computer problems caused by anything from spyware being installed without your knowledge to intruders taking control of your computer.
Ideally, computer users should evaluate the risks from the software they use. Many computers are sold with software already loaded. Whether installed by a computer manufacturer, operating system maker, Internet Service Provider, or by a retail store, the first step in assessing the vulnerability of your computer is to find out what software is installed and how one program will interact with another. Unfortunately, it is not practical for most people to perform this level of analysis.
There is an increasing threat from software attacks that take advantage of vulnerable web browsers. We have observed a trend whereby new software vulnerabilities are exploited and directed at web browsers through use of compromised or malicious web sites. This problem is made worse by a number of factors, including the following:
Ideally, computer users should evaluate the risks from the software they use. Many computers are sold with software already loaded. Whether installed by a computer manufacturer, operating system maker, Internet Service Provider, or by a retail store, the first step in assessing the vulnerability of your computer is to find out what software is installed and how one program will interact with another. Unfortunately, it is not practical for most people to perform this level of analysis.
There is an increasing threat from software attacks that take advantage of vulnerable web browsers. We have observed a trend whereby new software vulnerabilities are exploited and directed at web browsers through use of compromised or malicious web sites. This problem is made worse by a number of factors, including the following:
- Many users have a tendency to click on links without considering the risks of their actions.
- Web page addresses can be disguised or take you to an unexpected site.
- Many web browsers are configured to provide increased functionality at the cost of decreased security.
- New security vulnerabilities may have been discovered since the software was configured and packaged by the manufacturer.
- Computer systems and software packages may be bundled with additional software, which increases the number of vulnerabilities that may be attacked.
- Third-party software may not have a mechanism for receiving security updates.
- Many web sites require that users enable certain features or install more software, putting the computer at additional risk.
- Many users do not know how to configure their web browsers securely.
- Many users are unwilling to enable or disable functionality as required to secure their web browser.
As a result, exploiting vulnerabilities in web browsers has become a popular way for attackers to compromise computer systems.
II. Web Browser Features and Risks
It is important to understand the functionality and features of the web browser you use. Enabling some web browser features may lower security. Often, vendors will enable features by default to improve the computing experience, but these features may end up increasing the risk to the computer.
Attackers focus on exploiting client-side systems (your computer) through various vulnerabilities. They use these vulnerabilities to take control of your computer, steal your information, destroy your files, and use your computer to attack other computers. A low-cost way attackers do this is by exploiting vulnerabilities in web browsers. An attacker can create a malicious web page that will install TROJAN software or spyware that will steal your information. Additional information about spyware is available in the following document: Rather than actively targeting and attacking vulnerable systems, a malicious web site can passively compromise systems as the site is visited. A malicious HTML document can also be emailed to victims. In these cases, the act of opening the email or attachment can compromise the system.
Some specific web browser features and associated risks are briefly described below. Understanding what different features do will help you understand how they affect your web browser's functionality and the security of your computer.
ActiveX is a technology used by Microsoft Internet Explorer on Microsoft Windows systems. ActiveX allows applications or parts of applications to be utilized by the web browser. A web page can use ActiveX components that may already reside on a Windows system, or a site may provide the component as a downloadable object. This gives extra functionality to traditional web browsing, but may also introduce more severe vulnerabilities if not properly implemented
Attackers focus on exploiting client-side systems (your computer) through various vulnerabilities. They use these vulnerabilities to take control of your computer, steal your information, destroy your files, and use your computer to attack other computers. A low-cost way attackers do this is by exploiting vulnerabilities in web browsers. An attacker can create a malicious web page that will install TROJAN software or spyware that will steal your information. Additional information about spyware is available in the following document: Rather than actively targeting and attacking vulnerable systems, a malicious web site can passively compromise systems as the site is visited. A malicious HTML document can also be emailed to victims. In these cases, the act of opening the email or attachment can compromise the system.
Some specific web browser features and associated risks are briefly described below. Understanding what different features do will help you understand how they affect your web browser's functionality and the security of your computer.
ActiveX is a technology used by Microsoft Internet Explorer on Microsoft Windows systems. ActiveX allows applications or parts of applications to be utilized by the web browser. A web page can use ActiveX components that may already reside on a Windows system, or a site may provide the component as a downloadable object. This gives extra functionality to traditional web browsing, but may also introduce more severe vulnerabilities if not properly implemented
"ActiveX has been plagued with various vulnerabilities and implementation issues. One problem with using ActiveX in a web browser is that it greatly increases the attack surface, or “attackability,” of a system. Installing any Windows application introduces the possibility of new ActiveX controls being installed"
Java is an object-oriented programming language that can be used to develop active content for web sites. A Java Virtual Machine, or JVM, is used to execute the Java code, or “applet,” provided by the web site. Some operating systems come with a JVM, while others require a JVM to be installed before Java can be used. Java applets are operating system independent.
Java applets usually execute within a “sandbox” where the interaction with the rest of the system is limited. However, various implementations of the JVM contain vulnerabilities that allow an applet to bypass these restrictions. Signed Java applets can also bypass sandbox restrictions, but they generally prompt the user before they can execute. You can search the Vulnerability Notes Database for Java vulnerabilities at http://www.kb.cert.org/vuls/byid?searchview&query=java.
Plug-ins are applications intended for use in the web browser. Netscape has developed the NPAPI standard for developing plug-ins, but this standard is used by multiple web browsers, including Mozilla Firefox and Safari. Plug-ins are similar to ActiveX controls but cannot be executed outside of a web browser. Adobe Flash is an example of an application that is available as a plug-in.
Plug-ins can contain programming flaws such as buffer overflows, or they may contain design flaws such as cross-domain violations, which arises when the same origin policy is not followed.
Cookies are files placed on your system to store data for specific web sites. A cookie can contain any information that a web site is designed to place in it. Cookies may contain information about the sites you visited, or may even contain credentials for accessing the site. Cookies are designed to be readable only by the web site that created the cookie. Session cookies are cleared when the browser is closed, and persistent cookies will remain on the computer until the specified expiration date is reached.
Cookies can be used to uniquely identify visitors of a web site, which some people consider a violation of privacy. If a web site uses cookies for authentication, then an attacker may be able to acquire unauthorized access to that site by obtaining the cookie. Persistent cookies pose a higher risk than session cookies because they remain on the computer longer.
JavaScript, also known as ECMAScript, is a scripting language that is used to make web sites more interactive. There are specifications in the JavaScript standard that restrict certain features such as accessing local files.
VBScript is another scripting language that is unique to Microsoft Windows Internet Explorer. VBScript is similar to JavaScript, but it is not as widely used in web sites because of limited compatibility with other browsers.
The ability to run a scripting language such as JavaScript or VBScript allows web page authors to add a significant amount of features and interactivity to a web page. However, this same capability can be abused by attackers. The default configuration for most web browsers enables scripting support, which can introduce multiple vulnerabilities, such as the following:
Java applets usually execute within a “sandbox” where the interaction with the rest of the system is limited. However, various implementations of the JVM contain vulnerabilities that allow an applet to bypass these restrictions. Signed Java applets can also bypass sandbox restrictions, but they generally prompt the user before they can execute. You can search the Vulnerability Notes Database for Java vulnerabilities at http://www.kb.cert.org/vuls/byid?searchview&query=java.
Plug-ins are applications intended for use in the web browser. Netscape has developed the NPAPI standard for developing plug-ins, but this standard is used by multiple web browsers, including Mozilla Firefox and Safari. Plug-ins are similar to ActiveX controls but cannot be executed outside of a web browser. Adobe Flash is an example of an application that is available as a plug-in.
Plug-ins can contain programming flaws such as buffer overflows, or they may contain design flaws such as cross-domain violations, which arises when the same origin policy is not followed.
Cookies are files placed on your system to store data for specific web sites. A cookie can contain any information that a web site is designed to place in it. Cookies may contain information about the sites you visited, or may even contain credentials for accessing the site. Cookies are designed to be readable only by the web site that created the cookie. Session cookies are cleared when the browser is closed, and persistent cookies will remain on the computer until the specified expiration date is reached.
Cookies can be used to uniquely identify visitors of a web site, which some people consider a violation of privacy. If a web site uses cookies for authentication, then an attacker may be able to acquire unauthorized access to that site by obtaining the cookie. Persistent cookies pose a higher risk than session cookies because they remain on the computer longer.
JavaScript, also known as ECMAScript, is a scripting language that is used to make web sites more interactive. There are specifications in the JavaScript standard that restrict certain features such as accessing local files.
VBScript is another scripting language that is unique to Microsoft Windows Internet Explorer. VBScript is similar to JavaScript, but it is not as widely used in web sites because of limited compatibility with other browsers.
The ability to run a scripting language such as JavaScript or VBScript allows web page authors to add a significant amount of features and interactivity to a web page. However, this same capability can be abused by attackers. The default configuration for most web browsers enables scripting support, which can introduce multiple vulnerabilities, such as the following:
- Cross-Site Scripting
Cross-Site Scripting, often referred to as XSS, is a vulnerability in a web site that permits an attacker to leverage the trust relationship that you have with that site.
- Cross-Zone and Cross-Domain Vulnerabilities
Most web browsers employ security models to prevent script in a web site from accessing data in a different domain. These security models are primarily based on the Netscape Same Origin Policy: http://www.mozilla.org/projects/security/components/same-origin.html. Internet Explorer also has a policy to enforce security zone separation: http://www.microsoft.com/windows/ie/ie6/using/howto/security/setup.mspx.
Vulnerabilities that violate these security models can be used to perform actions that a site could not normally perform. The impact can be similar to a cross-site scripting vulnerability. However, if a vulnerability allows for an attacker to cross into the local machine zone or other protected areas, the attacker may be able to execute arbitrary commands on the vulnerable system.
- Detection evasion
Anti-virus, Intrusion Detection Systems (IDS), and Intrusion Prevention Systems (IPS) generally work by looking for specific patterns in content. If a “known bad” pattern is detected, then the appropriate actions can take place to protect the user. But because of the dynamic nature of programming languages, scripting in web pages can be used to evade such protective systems.
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