From: CERT Advisory (cert-advisorycert.org)
Date: Mon Aug 11 2003 - 21:21:05 CDT

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CERT Advisory CA-2003-20 W32/Blaster worm

   Original issue date: August 11, 2003
   Last revised: --
   Source: CERT/CC

   A complete revision history is at the end of this file.

Systems Affected

     * Microsoft Windows NT 4.0
     * Microsoft Windows 2000
     * Microsoft Windows XP
     * Microsoft Windows Server 2003

Overview

   The CERT/CC is receiving reports of widespread activity related to a
   new piece of malicious code known as W32/Blaster. This worm appears to
   exploit known vulnerabilities in the Microsoft Remote Procedure Call
   (RPC) Interface.

I. Description

   The W32/Blaster worm exploits a vulnerability in Microsoft's DCOM RPC
   interface as described in VU#568148 and CA-2003-16. Upon successful
   execution, the worm attempts to retrieve a copy of the file
   msblast.exe from the compromising host. Once this file is retrieved,
   the compromised system then runs it and begins scanning for other
   vulnerable systems to compromise in the same manner. In the course of
   propagation, a TCP session to port 135 is used to execute the attack.
   However, access to TCP ports 139 and 445 may also provide attack
   vectors and should be considered when applying mitigation strategies.
   Microsoft has published information about this vulnerability in
   Microsoft Security Bulletin MS03-026.

   Lab testing has confirmed that the worm includes the ability to launch
   a TCP SYN flood denial-of-service attack against windowsupdate.com. We
   are investigating the conditions under which this attack might
   manifest itself. Unusual or unexpected traffic to windowsupdate.com
   may indicate an infection on your network, so you may wish to monitor
   network traffic.

   Sites that do not use windowsupdate.com to manage patches may wish to
   block outbound traffic to windowsupdate.com. In practice, this may be
   difficult to achieve, since windowsupdate.com may not resolve to the
   same address every time. Correctly blocking traffic to
   windowsupdate.com will require detailed understanding of your network
   routing architecture, system management needs, and name resolution
   environment. You should not block traffic to windowsupdate.com without
   a thorough understanding of your operational needs.

   We have been in contact with Microsoft regarding this possibility of
   this denial-of-service attack.

II. Impact

   A remote attacker could exploit these vulnerabilities to execute
   arbitrary code with Local System privileges or to cause a
   denial-of-service condition.

III. Solutions

Apply patches

   All users are encouraged to apply the patches referred to in Microsoft
   Security Bulletin MS03-026 as soon as possible in order to mitigate
   the vulnerability described in VU#568148. These patches are also
   available via Microsoft's Windows Update service.

   Systems running Windows 2000 may still be vulnerable to at least a
   denial-of-service attack via VU#326746 if their DCOM RPC service is
   available via the network. Therefore, sites are encouraged to use the
   packet filtering tips below in addition to applying the patches
   supplied in MS03-026.

   It has been reported that some affected machines are not able to stay
   connected to the network long enough to download patches from
   Microsoft. For hosts in this situation, the CERT/CC recommends the
   following:
    1. Physically disconnecting the system from the network
    2. Check the system for signs of compromise.
          + In most cases, an infection will be indicated by the presence
            of the registry key
            "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion
            \Run\windows auto update" with a value of msblast.exe. If
            this key is present, remove it using a registry editor.
    3. If you're infected, terminate the running copy of msblast.exe
       using the Task Manager.
    4. Take one of the following steps to protect against the compromise
       prior to installing the Microsoft patch:
          + Disable DCOM as described below
          + Enabling Microsoft's Internet Connection Filter (ICF), or
            another host-level packet filtering program to block incoming
            connections for 135/tcp
    5. Reconnect the system to the network and apply the patches in the
       recommended manner

   Trend Micro, Inc. has published a set of steps to accomplish these
   goals. Symantec has also published a set of steps to accomplish these
   goals.

Disable DCOM

   Depending on site requirements, you may wish to disable DCOM as
   described in MS03-026. Disabling DCOM will help protect against this
   vulnerability but may also cause undesirable side effects. Additional
   details on disabling DCOM and possible side effects are available in
   Microsoft Knowledge Base Article 825750.

Filter network traffic

   Sites are encouraged to block network access to the following relevant
   ports at network borders. This can minimize the potential of
   denial-of-service attacks originating from outside the perimeter. The
   specific services that should be blocked include
     * 69/UDP
     * 135/TCP
     * 135/UDP
     * 139/TCP
     * 139/UDP
     * 445/TCP
     * 445/UDP
     * 4444/TCP

   Sites should consider blocking both inbound and outbound traffic to
   these ports, depending on network requirements, at the host and
   network level. Microsoft's Internet Connection Firewall can be used to
   accomplish these goals.

   If access cannot be blocked for all external hosts, the CERT/CC
   recommends limiting access to only those hosts that require it for
   normal operation. As a general rule, the CERT/CC recommends filtering
   all types of network traffic that are not required for normal
   operation.

   Because current exploits for VU#568148 create a backdoor, which is in
   some cases 4444/TCP, blocking inbound TCP sessions to ports on which
   no legitimate services are provided may limit intruder access to
   compromised hosts.

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

Reporting

   The CERT/CC is tracking activity related to this worm as CERT#30479.
   Relevant artifacts or activity can be sent to certcert.org with the
   appropriate CERT# in the subject line.

Appendix A. Vendor Information

   This appendix contains information provided by vendors. When vendors
   report new information, this section is updated and the changes are
   noted in the revision history. If a vendor is not listed below, we
   have not received their comments.

Microsoft

     Please see Microsoft Security Bulletin MS03-026.

Appendix B. References

     * CERT/CC Advisory CA-2003-19 -
       http://www.cert.org/advisories/CA-2003-19.html
     * CERT/CC Vulnerability Note VU#561284 -
       http://www.kb.cert.org/vuls/id/561284
     * CERT/CC Vulnerability Note VU#326746 -
       http://www.kb.cert.org/vuls/id/326746
     * Microsoft Security Bulletin MS03-026 -
       http://microsoft.com/technet/security/bulletin/MS03-026.asp
     * Microsoft Knowledge Base article 823980 -
       http://support.microsoft.com?kbid=823980

Thanks

   Our thanks to Microsoft Corporation for their review of and input to
   this advisory.
   ______________________________________________________________________

   Authors: Chad Dougherty, Jeffrey Havrilla, Shawn Hernan, and Marty
   Lindner
   ______________________________________________________________________

   This document is available from:
   http://www.cert.org/advisories/CA-2003-20.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
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   Copyright 2003 Carnegie Mellon University.

   Revision History

   August 11, 2003: Initial release

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