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Continuing threats to home users

CERT Advisory CA-2001-20 Continuing Threats to Home Users

   Original release date: July 20, 2001
   Last revised: July 23, 2001
   Source: CERT/CC
   A complete revision history can be found at the end of this file.
Need to Protect Home Systems

   This year, we have seen a significant increase in activity resulting
   in compromises of home user machines. In many cases, these machines
   are then used by intruders to launch attacks against other
   organizations. Home users have generally been the least prepared to
   defend against attacks. Many home users do not keep their machines up
   to date with security patches and workarounds, do not run current
   anti-virus software, and do not exercise caution when handling email
   attachments. Intruders know this, and we have seen a marked increase
   in intruders specifically targeting home users who have cable modem
   and DSL connections.
   Most of the subscribers to the CERT Advisory Mailing List and many
   visitors to our web site are technical staff responsible for
   maintaining systems and networks. But all of us know people who have
   home computers and need advice about how to secure them. We recently
   released a document on our web site providing some basic security
   information and references for home users. The document, "Home Network
   Security," is available on our web site at
   We encourage the technical readers of our mailing list to reach out to
   your parents, children, and other relatives and friends who might not
   be as technically oriented, point them to this document and help them
   understand the basics of security, the risks, and how they can better
   defend themselves. We have a long road to travel in educating home
   users on the security risks of the Internet. But all of us working
   together to educate home users will improve the security of the
   Internet as a whole.
Worms and DDoS Tools

   The CERT/CC is currently tracking the activity of several large-scale
   incidents involving new worms and distributed denial-of-service (DDoS)
   tools. Some of these worms include a command and control structure
   that allows the intruder to dynamically modify the behavior of the
   worm after it has infected a victim system. In some cases, the command
   and control structure allows the intruder to issue a single command to
   all the infected systems without needing to know which systems have
   actually been infected. This ability to change the behavior of the
   worm (including wholesale replacement), makes it substantially more
   difficult to develop "one size fits all" solutions to the problem.
   Additionally, many of these worms have targeted home users as victims.
   With these facts in mind, and the large number of hosts involved in
   these incidents, it is imperative for everyone to take precautions to
   patch the vulnerabilities involved and recover compromised systems.
W32/Leaves worm

   The W32/Leaves worm, described in IN-2001-07 primarily affects systems
   that have been previously compromised by the SubSeven Trojan horse
   program. We have received reports that over 23,000 machines have been
   compromised by this worm. This worm includes functionality that allows
   a remote intruder to control the network of compromised machines.
"Code Red" worm

   The "Code Red" worm, described in CA-2001-19 exploits a vulnerability
   in the Indexing Service on systems running Microsoft IIS. Current
   reports indicate that over 250,000 hosts have already been compromised
   by this worm.
"Power" worm

   A worm, known by the name of "Power" is also compromising systems
   vulnerable to the IIS Unicode vulnerability described in VU#111677. It
   uses the Internet Relay Chat (IRC) as a control channel for
   coordinating compromised machines in DDoS attacks. Based on reports
   that we have received, over 10,000 machines have already been
   compromised by this worm.
"Knight" distributed attack tool

   An attack tool known as "Knight" has been found on approximately 1,500
   hosts. This tool appears to be a DDoS tool and also uses IRC as a
   control channel. It has been reported that the tool is commonly being
   installed on machines that were previously compromised by the
   BackOrifice Trojan horse program. So far, there has been no indication
   that this tool is a worm; it does not contain any logic to propagate
Protective Measures

   For all of these problems, the deployment and maintenance of some
   these simple defenses are relatively effective:
1. Install and Maintain Anti-Virus Software

   The CERT/CC strongly recommends using anti-virus software. Most
   current anti-virus software products are able to detect and alert the
   user that an intruder is attempting to install a Trojan horse program
   or that one has already been installed.
   In order to ensure the continued effectiveness of such products, it is
   important to keep them up to date with current virus and attack
   signatures supplied by the original vendors. Many anti-virus packages
   support automatic updates of virus definitions. We recommend using
   these automatic updates when available.
2. Deploy a Firewall

   The CERT/CC also recommends using a firewall product, such as a
   network appliance or a personal firewall software package. In some
   situations, these products may be able to alert users to the fact that
   their machine has been compromised. Furthermore, they have the ability
   to block intruders from accessing backdoors over the network. However,
   no firewall can detect or stop all attacks, so it is important to
   continue to follow safe computing practices.
   For additional information about securing home systems and networks,
   please see the "Home Network Security" tech tip at
   If these protective measures reveal that the machine has already been
   compromised, more drastic steps need to be taken to recover. When a
   computer is compromised, any installed software could have been
   modified, including the operating system, applications, data files,
   and memory. In general, the only way to ensure that a compromised
   computer is free from backdoors and intruder modifications is to
   re-install the operating system from the distribution media and
   install vendor-recommended security patches before connecting back to
   the network. Merely identifying and fixing the vulnerability that was
   used to initially compromise the machine may not be enough.
   Often, these worms rely on Trojan horses to initially compromise a
   system. For more information on Trojan horses, see
   Additionally, these worms often spread by exploiting vulnerabilities
   in systems. For information on vulnerabilities affecting popular
   products, please see
   Author(s): Jeff Carpenter, Chad Dougherty, Shawn Hernan
   This document is available from:
CERT/CC Contact Information

   Email: cert@cert.org
          Phone: +1 412-268-7090 (24-hour hotline)
          Fax: +1 412-268-6989
          Postal address:
          CERT Coordination Center
          Software Engineering Institute
          Carnegie Mellon University
          Pittsburgh PA 15213-3890
   CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) /
   EDT(GMT-4) Monday through Friday; they are on call for emergencies
   during other hours, on U.S. holidays, and on weekends.
Using encryption

   We strongly urge you to encrypt sensitive information sent by email.
   Our public PGP key is available from
   If you prefer to use DES, please call the CERT hotline for more
Getting security information

   CERT publications and other security information are available from
   our web site
   To subscribe to the CERT mailing list for advisories and bulletins,
   send email to majordomo@cert.org. Please include in the body of your
   subscribe cert-advisory
   * "CERT" and "CERT Coordination Center" are registered in the U.S.
   Patent and Trademark Office.
   Any material furnished by Carnegie Mellon University and the Software
   Engineering Institute is furnished on an "as is" basis. Carnegie
   Mellon University makes no warranties of any kind, either expressed or
   implied as to any matter including, but not limited to, warranty of
   fitness for a particular purpose or merchantability, exclusivity or
   results obtained from use of the material. Carnegie Mellon University
   does not make any warranty of any kind with respect to freedom from
   patent, trademark, or copyright infringement.
   Conditions for use, disclaimers, and sponsorship information
   Copyright 2001 Carnegie Mellon University.
   Revision History
Jul 20, 2001: Initial release
Jul 23, 2001: Correct link to the IIS Unicode vulnerability in Power worm secti

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