Net-Worm.Win32.IISWorm

Parent class: VirWare

Viruses and worms are malicious programs that self-replicate on computers or via computer networks without the user being aware; each subsequent copy of such malicious programs is also able to self-replicate. Malicious programs which spread via networks or infect remote machines when commanded to do so by the “owner” (e.g. Backdoors) or programs that create multiple copies that are unable to self-replicate are not part of the Viruses and Worms subclass. The main characteristic used to determine whether or not a program is classified as a separate behaviour within the Viruses and Worms subclass is how the program propagates (i.e. how the malicious program spreads copies of itself via local or network resources.) Most known worms are spread as files sent as email attachments, via a link to a web or FTP resource, via a link sent in an ICQ or IRC message, via P2P file sharing networks etc. Some worms spread as network packets; these directly penetrate the computer memory, and the worm code is then activated. Worms use the following techniques to penetrate remote computers and launch copies of themselves: social engineering (for example, an email message suggesting the user opens an attached file), exploiting network configuration errors (such as copying to a fully accessible disk), and exploiting loopholes in operating system and application security. Viruses can be divided in accordance with the method used to infect a computer:

• file viruses
• boot sector viruses
• macro viruses
• script viruses

Any program within this subclass can have additional Trojan functions. It should also be noted that many worms use more than one method in order to spread copies via networks.

Class: Net-Worm

Net-Worms propagate via computer networks. The distinguishing feature of this type of worm is that it does not require user action in order to spread. This type of worm usually searches for critical vulnerabilities in software running on networked computers. In order to infect the computers on the network, the worm sends a specially crafted network packet (called an exploit) and as a result the worm code (or part of the worm code) penetrates the victim computer and activates. Sometimes the network packet only contains the part of the worm code which will download and run a file containing the main worm module. Some network worms use several exploits simultaneously to spread, thus increasing the speed at which they find victims.

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Platform: Win32

Win32 is an API on Windows NT-based operating systems (Windows XP, Windows 7, etc.) that supports execution of 32-bit applications. One of the most widespread programming platforms in the world.

Description

Technical Details

This is the first known worm intending to target Web sites by infecting Internet Information Servers (ISS). The worm realizes its method of spreading from one Web site to other Web sites by sending and executing its EXE file. The name of the worm file is constant - IISWORM.EXE.

The worm infects only machines with an installed IIS package and Web-site contents. The worm application being run on a such machine locates and infects remote Web sites (remote machines with installed IIS package): it enters them, and by using a trick, sends its copy to there, and spawns that copy in there. As a result, the worm infects all Web servers that can be accessed from the currently infected machine, and other infected servers spread the worm copy further etc.

A similar way of infection was used by the famous "Morris virus" (a.k.a. "Internet worm") that hit USA networks back in 1988. That worm infected several thousand machines and paralyzed many networks because of unlimited copies sent. Fortunately, the "IISWorm" has a lethal bug and cannot repeat that story. The worm seems to be able to spread its copy to the first IIS machine, but fails to spread itself further.

The worm code contains only spreading routines, not trigger ones. The worm does not manifest itself in any way.

Details

The worm itself is a Win32 application about 80K in length, written in Borland C++. It is executed as a standard Windows application, opens a connection and uses an HTTP-packets format to spread itself.

To locate victim servers, the worm looks for Web-site addresses in all *.HTM* files in the INetpub directories:

wwwroot
www root
inetpubwwwroot
inetpubwww root
websharewwwroot

By using Web-site addresses, the worm connects them and sends a bomb package to there. This package exploits a vulnerability in IIS software - the package is constructed so that its data overlaps a data buffer on a remote IIS, and a block of the package is executed as code in there (at a remote IIS). This piece of code opens a connection to its "parent" machine, gets the complete copy of the worm (the IISWORM.EXE file), creates it on a disk and spawns. As a result, the remote IIS machine is infected and the worm is active in it and continues spreading.

During tests in the lab, there were some mistakes found in the worm code that prevent the worm from spreading. The worm seems also to be dependent on the IIS and WinNT ServicePack versions.

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Find out the statistics of the vulnerabilities spreading in your region on statistics.securelist.com