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10.1. Introduction

Exploits, vulnerabilities1, and buffer overflow techniques2 have long been used by malicious hackers and virus writers. Until recently, however, these techniques were not commonplace. The CodeRed3, 4 worm was a major shock to the antivirus industry because it was the first worm that spread not as a file but solely in memory by utilizing a buffer overflow in Microsoft IIS. Many antivirus companies were unable to provide protection against CodeRed, while other companies with a wider focus on security could provide solutionsto the relief of end users.

Usually new techniques are picked up and used by copycat virus writers. Thus, many similarly successful worms followed CodeRed, such as Nimda5 and Badtrans6.

This chapter covers not only such techniques as buffer overflows and input validation exploits, but also how computer viruses are using them to their advantage.

10.1.1. Definition of Blended Attack

A blended threat is often referred to as a blended attack7. Some people refer to it as a combined attack or a mixed technique. Without attempting to make a strong definition here, I will say simply that, in the context of computer viruses, this term is typically used when the virus exploits some sort of security flaw of a system or an application to invade new systems. A blended threat exploits one or more vulnerabilities as the main vector of infection and might perform additional network attacks, such as a denial of service (DoS) attack, against other systems.

10.1.2. The Threat

Security exploits, commonly used by malicious hackers, are being combined with computer viruses, resulting in very complex attacks that sometimes go beyond the general scope of antivirus software.

In general, a large gap has existed between computer security companies, such as intrusion detection and firewall vendors and antivirus companies. For example, many past popular computer security conferences did not have any papers or presentations dealing with computer viruses. Some computer security people do not seem to consider computer viruses a serious aspect of security, or they ignore the relationship between computer security and computer viruses.

When the CodeRed worm appeared, there was obvious confusion about which kind of computer security vendors could prevent, detect, and stop the worm. Some antivirus researchers argued that there was nothing they could do about CodeRed; others tried to solve the problem with various sets of security techniques, software, and detection tools to support their customers' needs.

Interestingly, such intermediate solutions were often criticized by antivirus researchers. Instead of realizing that affected customers needed such tools, some antivirus researchers suggested that there was nothing to do but to install the security patch.

Obviously, this step is very important in securing the systems. At large corporations, however, the installation of a patch on thousands of systems might not be easy to deliver, especially so in lack of centralized patch management. Furthermore, corporations might have the valid fear that new patches could introduce a new set of problems, compromising system stability.

CodeRedand blended attacks in generalis a problem that must be addressed both by antivirus vendors and by other security product vendors so that multilayered security solutions can be delivered in a combined effort to deal with blended attacks.

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