Networking / Beginners

Dangers Associated with Using ActiveX

The primary dangers associated with using ActiveX controls stem from the way Microsoft approaches security. By using their Authenticode technology to digitally sign an ActiveX control, Microsoft attempts to guarantee the user of the origin of the control and that it has not been tampered with since it was created. In most cases this works, but there are several things that Microsoft's authentication system does not do, which can pose a serious threat to the security of an individual machine and a network.

The first and most obvious danger is that Microsoft does not limit the access that the control has after it is installed on a local machine.This is one of the key differences between ActiveX and Java. Java uses a method known as sandboxing. Sandboxing a Java applet ensures that the application is running in its own protected memory area, which isolates it from things like the file system and other applications.The restrictions put on Java applets prevent malicious code from gaining access to an OS or network, and thwarts untrusted sources from harming the system.

ActiveX controls, on the other hand, have the same rights as the user who is running them after they are installed on a computer. Microsoft does not guarantee that the author is the one using the control, or that it is being used in the way it was intended, or on the site or pages for which it was intended. Microsoft also cannot guarantee that the owner of the site or someone else has not modified the pages since the control was put in place. It is the exploitation of these vulnerabilities that poses the greatest dangers associated with using ActiveX controls.

Symantec's Web site reports that the number of ActiveX vulnerabilities over the last few years have increased dramatically, with those affecting ActiveX controls shipped by vendors increasing upwards of 300 percent. From 2002 to 2005, there was a range of 12 to 15 vulnerabilities affecting ActiveX controls found each year, but in 2006, this number jumped to 50. While it would be nice to think that all of these are due to inexperienced programmers who aren't observing best practices in coding, even Microsoft has shipped a number of vulnerable controls over the years.

The vulnerabilities that have occurred over the years include major issues that could be exploited by hackers. For example, in 2006, vulnerabilities were found in Microsoft's XML Core Services that provided hackers with the ability to run remote code on affected systems. If a hacker wrote code on a Web page to exploit this vulnerability, he or she could gain access to a visiting computer.The hacker would be able to run code remotely on the user's computer, and have the security associated with that user. In other words, if the user was logged in as an administrator to the computer, the hacker could add, delete, and modify files, create new accounts, and so on. Although a security update was released in October 2006 that remedied the problem, anyone without the security update applied to his or her system could still be affected. It just goes to show that every time a door is closed to a system, a hacker will find a way to kick in a window.

Avoiding Common ActiveX Vulnerabilities

One of the most common vulnerabilities with ActiveX controls has to do with the programmer's perception, or lack thereof, of the capabilities of the control. Every programmer that works for a company or consulting firm and writes a control for a legitimate business use wants his controls to be as easy to use as possible. He takes into consideration the intended use of the control, and if it seems OK, he marks it "safe-for-scripting." Programmers set the Safe for Scripting flag so their ActiveX controls aren't checked for an Authenticode signature before being run. By enabling Safe for Scripting, code checking is bypassed, and the control can be run without the user being aware of a problem. As you can see, this is a double-edged sword. If it is not marked "safe," users will be inundated with warnings and messages on the potential risk of using a control that is not signed or not marked as safe. Depending on the security settings in the browser, they may not be allowed to run it at all. However, after it is marked as safe, other applications and controls have the ability to execute the control without requesting the user's approval.You can see how this situation could be dangerous. A good example of the potential effects of ActiveX is the infamous Windows Exploder control.This was a neat little ActiveX control written by Fred McLain ( that demonstrates what he calls "dangerous" technology. His control only performs a clean shutdown and power-off of the affected Windows system.This might not seem so bad, but it was written that way to get the point across that the control could be used to perform much more destructive acts. Programmers have to be careful with ActiveX controls, and be sure that they know everything their control is capable of before releasing it.

Another problem that arises as a result of lack of programmer consideration is the possibility that a control will be misused and at the same time take advantage of the users' privileges. Just because the administrator has a specific use in mind for a control does not mean that someone else cannot find a different use for the control.There are many people who are not trustworthy and will try to exploit another's creativity.

Another common cause of vulnerabilities in ActiveX controls is the release of versions that have not been thoroughly tested and contain bugs. One specific bug that is often encountered in programs is the buffer overflow bug. As we'll discuss more fully later in this tutorial, buffer overflows occur when a string is copied into a fixed-length array and the string is larger than the array.The result is a buffer overflow and a potential application crash.With this type of error, the key is that the results are unpredictable.The buffer overflow may print unwanted characters on the screen, or it may kill the browser and in turn lock up the system.This problem has plagued the UNIX/Linux world for years, and in recent years has become more noticeable on the Windows platform. If you browse the top IT security topics at Microsoft TechNet (, you will notice numerous buffer overflow vulnerabilities. In fact, at times, one or more issues involving this type of error were found monthly on the site. As mentioned, this is not exclusively a Microsoft problem, but it affects almost every vendor that writes code for the Windows platform.

To illustrate how far-reaching this type of problem has been, in a report found on the secureroot Web site (, Neal Krawetz reported that he had identified a buffer overflow condition in the Shockwave Flash plug-in for Web browsers. He states,"Macromedia's Web page claims that 90 percent of all Web browsers have the plug-ins installed. Because this overflow can be used to run arbitrary code, it impacts 90 percent of all Web-enabled systems." Now that is a scary thought! While this report was originally written in 2001, a similar error was reported on Adobe's Web site in 2006 regarding Shockwave Player when it is installed.This vulnerability also allowed malicious code to exploit a buffer overflow effort and allowed the execution of arbitrary code. Although buffer overflows are a widespread type of error, the solution is simple: Programmers must take the extra time required to do thorough testing and ensure that their code contains proper bounds checking on all values that accept variable length input.

Another vulnerability occurs when using older, retired versions of ActiveX controls. Some may have had errors, some not. Some may have been changed completely or replaced for some reason. After someone else has a copy of a control, it cannot be guaranteed that the current version will be used, especially if it can be exploited in some way. Although users will get an error message when they use a control that has an expired signature, a lot of people will install it anyway. Unfortunately, there is no way to prevent someone from using a control after it has been retired from service. After a control that can perform a potentially harmful task is signed and released, it becomes fair game for every hacker on the Internet. In this case, the best defense is a good offense.Thorough testing before releasing a control will save much grief later.

Lessening the Impact of ActiveX Vulnerabilities

An ActiveX vulnerability is serious business for network administrators, end users, and developers alike. For some, the results of misused or mismanaged ActiveX controls can be devastating; for others, it is never taken into consideration.There can be policies in place that disallow the use of all controls and scripts, but it has to be done at the individual machine level, and takes a lot of time and effort to implement and maintain.This is especially true in an environment where users are more knowledge able on how to change browser settings. Even when policy application can be automated throughout the network, this might not be a feasible solution if users need to be able to use some controls and scripts. Other options can limit the access of ActiveX controls, such as using firewalls and virus protection software, but the effectiveness is limited to the obvious and known. Although complete protection from the exploitation of ActiveX vulnerabilities is difficult-if not impossible-to achieve, users from every level can take steps to help minimize the risk.

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