Aliases

Net-Worm.Linux.Adm (Kaspersky Lab) is also known as: Worm.Linux.Adm (Kaspersky Lab), Linux/Adm.worm (McAfee),   Unix/AdmWorm (Sophos),   SH/Admworm.A* (RAV),   UNIX_ADMWORM.A (Trend Micro),   Unix/Admworm.A (FRISK),   UNIX:Malware (ALWIL),   Worm Generic (Panda)

Description added	May 31 2001
Behavior	Internet Worm

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".