From: CERT Advisory (cert-advisorycert.org)
Date: Tue Jan 27 2004 - 11:28:27 CST

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CERT Advisory CA-2004-02 Email-borne Viruses

   Original release date: January 27, 2004
   Last revised: --
   Source: CERT/CC

   A complete revision history can be found at the end of this file.

Systems Affected

     * Any system running Microsoft Windows (all versions from Windows 95
       and up) and used for reading email or accessing peer-to-peer file
       sharing services.

Overview

   In recent weeks there have been several mass-mailing viruses released
   on the Internet. It is important for users to understand the risks
   posed by these pieces of malicious code and the steps necessary to
   protect their systems from virus infection.

I. Description

   Over the past week, we have seen two more mass-mailing viruses,
   W32/Bagle and W32/Novarg, impact a significant number of home users
   and sites. The technology used in these viruses is not significantly
   different from prior mass-mailing viruses such as W32/Sobig and
   W32/Mimail. Unsolicited email messages containing attachments are sent
   to unsuspecting recipients. They may contain a return address, a
   provocative envelope, or something else that encourages its receiver
   to open it. This technique is called social engineering. Because we
   are trusting and curious, social engineering is often effective. The
   widespread impact of these latest viruses, which rely on human
   intervention to spread, demonstrates the effectiveness of social
   engineering.
       
   It continues to be important to ensure that anti-virus software is
   used and updated regularly, that attachments are examined on mail
   servers, and that firewalls filter unneeded ports and protocols. It
   also remains necessary that users be educated about the dangers of
   opening attachments, especially executable attachments.

       CERT Incident Note IN-2004-01 - W32/Novarg
       http://www.cert.org/incident_notes/IN-2004-01.html

       CERT Incident Note IN-2003-03 - W32/Sobig.F
       http://www.cert.org/incident_notes/IN-2003-03.html

       CERT Incident Note IN-2003-02 - W32/Mimail
       http://www.cert.org/incident_notes/IN-2003-02.html

II. Impact

   A virus infection can have significant consquences on your computer
   system. These consequences include, but are not limited to:

     * Information disclosure - Mass-mailing viruses typically harvest
       email addresses from the addressbooks or files found on an
       infected system. Some viruses will also attempt to send files from
       an infected host to other potential victims or even back to the
       virus author. These files may contain sensitive information.

     * Add/Modify/Delete files - Once a system is compromised, a virus
       could potentially add, modify or delete arbitrary files on the
       system. These files may contain personal information or be
       required for the proper operation of the computer system.

     * Affect system stability - Viruses can consume significant amounts
       of computer resources causing a system to run slowly or be
       rendered unusable.

     * Install a backdoor - Many viruses will install a backdoor on an
       infected system. This backdoor may be used by a remote attacker to
       gain access to the system, or view/add/modify/delete files on the
       system. These backdoors may also be leveraged to download and
       control additional tools for use in distributed denial-of-service
       (DDoS) attacks against other sites.

     * Attack other systems - Systems infected by viruses are frequently
       used to attack other systems. These attacks frequently involve
       attempts to exploit vulnerabilities on the remote systems or
       denial-of-service attacks that utilize a high volume of network
       traffic.

     * Send unsolicited bulk email (spam) to other users - There have
       been numerous reports of spammers leveraging compromised systems
       to send unsolicited bulk email. Frequently these compromised
       systems are poorly protected end user computers (e.g., home and
       small business systems).

III. Solution

   In addition to following the steps outlined in this section, the
   CERT/CC encourages home users to review the "Home Network Security"
   and "Home Computer Security" documents.

       Home Network Security
       http://www.cert.org/tech_tips/home_networks.html

       Home Computer Security
       http://www.cert.org/homeusers/HomeComputerSecurity/

Run and maintain an anti-virus product

   While an up-to-date antivirus software package cannot protect against
   all malicious code, for most users it remains the best first line of
   defense against malicious code attacks. Users may wish to read
   IN-2003-01 for more information on anti-virus software and security
   issues.

       CERT Incident Note IN-2003-01
       http://www.cert.org/incident_notes/IN-2003-01.html

   Most antivirus software vendors release frequently updated
   information, tools, or virus databases to help detect and recover from
   malicious code. Therefore, it is important that users keep their
   antivirus software up to date. The CERT/CC maintains a partial list of
   antivirus vendors.
   
       Computer Virus Resources
       http://www.cert.org/other_sources/viruses.html

   Many antivirus packages support automatic updates of virus
   definitions. The CERT/CC recommends using these automatic updates when
   available.

Do not run programs of unknown origin

   Do not download, install, or run a program unless you know it to be
   authored by a person or company that you trust.

   Email users should be wary of unexpected attachments. Be sure you know
   the source of an attachment before opening it. Also remember that it
   is not enough that the mail originated from an email address you
   recognize. The Melissa virus spread precisely because it originated
   from a familiar email address.

   Users should also be wary of URLs in email messages. URLs can link to
   malicious content that in some cases may be executed without user
   intervention. A common social engineering technique known as
   "phishing" uses misleading URLs to entice users to visit malicious web
   sites. These sites spoof legitimate web sites to solicit sensitive
   information such as passwords or account numbers.

   In addition, users of Internet Relay Chat (IRC), Instant Messaging
   (IM), and file-sharing services should be particularly careful of
   following links or running software sent to them by other users. These
   are commonly used methods among intruders attempting to build networks
   of distributed denial-of-service (DDoS) agents.

Use a personal firewall

   A personal firewall will not necessarily protect your system from an
   email-borne virus, but a properly configured personal firewall may
   prevent the virus from downloading additional components or launching
   attacks against other systems. Unfortunately, once on a system, a
   virus may be able to disable a software firewall, thus eliminating its
   protection.

Email gateway filtering

   Depending on your business requirements, it is advisable to configure
   filtering of specific file extensions of email attachments at the
   email gateway. This filtering should be configured carefully, as this
   may affect legitimate attachments as well. It is recommended that
   attachments are quarantined for later examination and/or possible
   retrieval.

Recovering from a system compromise

   If you believe a system under your administrative control has been
   compromised, please follow the steps outlined in

       Steps for Recovering from a UNIX or NT System Compromise
       http://www.cert.org/tech_tips/win-UNIX-system_compromise.html
     _________________________________________________________________

   Authors: Jeff Carpenter, Chad Dougherty, Jeff Havrilla, Allen
   Householder, Brian King, Marty Lindner, Art Manion, Damon Morda, Rob
   Murawski
   ______________________________________________________________________

   This document is available from:
   http://www.cert.org/advisories/CA-2004-02.html
   ______________________________________________________________________

CERT/CC Contact Information

   Email: certcert.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
          U.S.A.

   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
   http://www.cert.org/CERT_PGP.key

   If you prefer to use DES, please call the CERT hotline for more
   information.

Getting security information

   CERT publications and other security information are available from
   our web site
   http://www.cert.org/

   To subscribe to the CERT mailing list for advisories and bulletins,
   send email to majordomocert.org. Please include in the body of your
   message

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   * "CERT" and "CERT Coordination Center" are registered in the U.S.
   Patent and Trademark Office.
   ______________________________________________________________________

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   Engineering Institute is furnished on an "as is" basis. Carnegie
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   ______________________________________________________________________

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   Copyright 2004 Carnegie Mellon University.

   Revision History
   January 27, 2004: Initial release

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