Net-Worm.Linux.Adm

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: Linux

Linux is a family of UNIX-influenced operating systems based on the Linux kernel and GNU tools.

Description

Technical Details

This is the worm infecting Linux systems. The worm was discovered in spring 1998. It spreads itself from system to system by using a Linux security breach (so called "buffer overrun" breach) that allows to upload to remote system and run there a short piece of code that then downloads and activates the main worm component.

The worm uses a security breach in the program package BIND (Berkeley Internet Name Domain), which is distributed in many popular UNIX packages and provides name service for the internet.

The Worm Itself

This is multi-component worm that consist of 8 files. These files are script programs and executable files. The script programs are ".sh" files that are run by Linux command shell. The executable files are standard Linux ELF executables.

The main components of the worm are script ".sh" files that are run as hosts, and then run the rest files (additional ".sh" files and ELF executables) to perform necessary actions.

The list of components looks as follows:

 ADMw0rm            Hnamed



 gimmeIP            remotecmd



 gimmeRAND          scanco



 incremental        test

Spreading

The spreading (infecting a remote Linux machine) is done by "buffer overrun" attack. That attack is performed as a special packet that is sent to a machine being attacked. The packet has a block of specially prepared data. That block of packet's data is then executed as a code on that machine. That code opens a connection to infected machine, gets the rest of worm code and activates it. At that moment the machine is infected, and starts to spread worm further.

The worm is transferred from a machine to machine as a "tgz" archive (standard UNIX archive) with "ADMw0rm.tgz" name, with 8 worm components inside. While infecting a new machine the worm unpacks that package in there, and runs the main "ADMw0rm" file that then will activate other worm's components.

Details

To get IP addresses of remote machines to attack them the worm scans the available global network for IP addresses with computers and DNS installed servers on it.

To attack remote system the worm uses security vulnerabilities in Linux demon: "named".

To upload and activate its copy on remote machine the worm "buffer overrun" code contains the instructions that switch to "root" privileges, runs command shell and follows the commands:

• runs the deamon "/usr/sbin/named"
• creates the directory to download the worm "tgz" file, the directory name is "/tmp/.w0rm0r"
• runs "ftp" (standart Linux program) that downloads worm "tgz" file from host machine (machine the worm is spreading from)
• unpacks all worm components from "tgz" archive
• runs the worm startup component: the "ADMw0rm" file

Misc.

The worm has several payload and other non-infection routines.

First of all it finds on local machine starting from root directory all "index.html" files (Web servers start pages) and replaces them with its own "index.html" file that contains the text:

The ADM Inet w0rm is here !

The worm deletes the "/etc/hosts.deny" file. That file contains the list of hosts (addresses and/or Inet names) that are denied to access this system (in case so-called TCP wrapper is used). As a result any of restricted machines can access affected system.

When a new system is infected, the worm sends "notification" messages to the e-mail address "admsmb@hotmail.com".

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