Information Security: Worms

   

Worms

A worm is a program that can replicate itself and send copies from computer to computer across network connections. Upon arrival, the worm may be activated to replicate and propagate again. In addition to propagation, the worm usually performs some unwanted function. A worm actively seeks out more machines to infect and each machine that is infected serves as an automated launching pad for attacks on other machines.

The concept of a computer worm was introduced in John Brunner’s 1975 SF novel The Shockwave Rider. The first known worm implementation was done in Xerox Palo Alto Labs in the early 1980s. It was nonmalicious, searching for idle systems to use to run a computationally intensive task.

Network worm programs use network connections to spread from system to system. Once active within a system, a network worm can behave as a computer virus or bacteria, or it could implant Trojan horse programs or perform any number of disruptive or destructive actions.

To replicate itself, a network worm uses some sort of network vehicle. Examples include the following:

·      Electronic mail facility: A worm mails a copy of itself to other systems, so that its code is run when the e-mail or an attachment is received or viewed. 


·      Remote execution capability: A worm executes a copy of itself on another system, either using an explicit remote execution facility or by exploiting a program flaw in a network service to subvert its operations. 


·      Remote login capability: A worm logs onto a remote system as a user and then uses commands to copy itself from one system to the other, where it then executes. 


The new copy of the worm program is then run on the remote system where, in addition to any functions that it performs at that system, it continues to spread in the same fashion. 
A network worm exhibits the same characteristics as a computer virus: a dormant phase, a propagation phase, a triggering phase, and an execution phase. The propagation phase generally performs the following functions:

1.     Search for other systems to infect by examining host tables or similar repositories of remote system addresses. 


2.     Establish a connection with a remote system. 


3.     Copy itself to the remote system and cause the copy to be run. 


Example: Internet Worm of 1988 targeted Berkeley, Sun UNIX systems entered the Internet; within hours, it had rendered several thousand computers unusable. It used virus-like attack to inject instructions into running program and run them. To recover from this the machines had to disconnect system from Internet and reboot. To prevent re-infection, several critical programs had to be patched, recompiled, and reinstalled. The only way to determine if the program had suffered other malicious side effects was to disassemble it. Fortunately, the only purpose of this virus turned out to be self-propagation.

Example: The Father Christmas worm was interesting because it was a form of macro worm. It was distributed in 1987 and was designed for IBM networks. It was an electronic letter instructing recipient to save it and run it as a program that drew Christmas tree, printed “Merry Christmas!” It also checked address book, list of previously received email and sent copies to each address. The worm quickly overwhelmed the IBM networks and forced the networks and systems to be shut down. This worm had the characteristics of a macro worm. It was written in a high-level job control language, which the IBM systems interpreted.

Worms with good intent

The Nachi family of worms, for example, tried to download and install patches from Microsoft's website to fix vulnerabilities in the host system — by exploiting those same vulnerabilities. In practice, although this may have made these systems more secure, it generated considerable network traffic, rebooted the machine in the course of patching it, and did its work without the consent of the computer's owner or user.

In 1982, at the Xerox Park research institute, a worm was created to find idle machines. It was used to distribute workloads and was not a malicious worm. So worms can be helpful.