__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN Blaster Worm (aka: W32.Blaster, MSBlast, Lovsan, Win32.Poza) [CERTŪ Advisory CA-2003-20] August 12, 2003 14:00 GMT Number N-133 ______________________________________________________________________________ PROBLEM: The Blaster worm exploits the Microsoft RPC DCOM vulnerability to propagate as described in CIAC Bulletin N-117. The purpose of this malicious code is to infect as many computers as possible to carry out a Distributed Denial of Service Attack against the web site www.windowsupdate.com, which has been coded in this worm to take place on August 16, 2003. PLATFORM: Microsoft Windows NT 4.0 Microsoft Windows 2000 Microsoft Windows XP Microsoft Windows Server 2003 DAMAGE: Once installed on a machine, Blaster scans random IP ranges, with the aim of finding more PCs to infect. In addition, it creates a file in the system called msblast.exe which contains the code of the worm. It creates a registry key to ensure it is started when the operating system is restarted. SOLUTION: Apply Microsoft patches as described in CIAC Bulletin N-117. Keep anti-virus definition files updated. ______________________________________________________________________________ VULNERABILITY The risk is HIGH. Blaster is a high-profile and fast-spreading ASSESSMENT: worm. A remote attacker could exploit the RPC/DCOM vulnerability to execute arbitrary code with Local System privileges or to cause a denial-of-service condition. ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/n-133.shtml ORIGINAL BULLETIN: http://www.cert.org/advisories/CA-2003-20.html ADDITIONAL MONITOR THE SITES BELOW FOR UPDATES INFORMATION: - Microsoft MS03-026: http://www.microsoft.com/technet/treeview/default.asp?url =/technet/security/bulletin/MS03-026.asp - Microsoft Knowledge Base article 823980 http://support.microsoft.com?kbid=823980 - DHS/FedCIRC Advisory FA-2003-20 http://www2.fedcirc.gov/advisories/FA-2003-20.html - Computer Associates - Win32.Poza worm http://www3.ca.com/solutions/collateral.asp?CT=27081&CID =48952 - F-Secure Lovsan, MSBlast, Blaster worm http://www.europe.f-secure.com/v-descs/msblast.shtml - ISS Xforce MSRPC DCOM Worm Propagation http://xforce.iss.net/xforce/alerts/id/150 - Network Associates - W32/Lovsan.worm http://vil.nai.com/vil/content/v_100547.htm - Panda Software's Virus Encyclopedia http://www.pandasoftware.com/virus_info/encyclopedia/ - Sophos - W32/Blaster-A worm http://www.sophos.com/support/disinfection/blastera.html - Symantec - W32.Blaster.Worm http://securityresponse.symantec.com/avcenter/venc/data/ w32.blaster.worm.html - Trend Micro - WORM_MSBLAST.A http://www.trendmicro.com/vinfo/virusencyclo/ default5.asp?VName=WORM_MSBLAST.A ______________________________________________________________________________ [***** Start CERTŪ Advisory CA-2003-20 *****] CERTŪ 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 cert@cert.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: 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 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 majordomo@cert.org. Please include in the body of your message subscribe cert-advisory * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office. NO WARRANTY 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 2003 Carnegie Mellon University. Revision History August 11, 2003: Initial release [***** End CERTŪ Advisory CA-2003-20 *****] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of CERT for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 925-422-8193 (7x24) FAX: +1 925-423-8002 STU-III: +1 925-423-2604 E-mail: ciac@ciac.org Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://www.ciac.org/ Anonymous FTP: ftp.ciac.org PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. 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