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Department of Homeland Security


Potential For Significant Impact On Internet Operations Due To Vulnerability In Microsoft Operating Systems

July 24, 2003

SYSTEMS AFFECTED: Computers using the following operating systems:

Microsoft Windows NT 4.0
Microsoft Windows NT 4.0 Terminal Services Edition
Microsoft Windows 2000
Microsoft Windows XP
Microsoft Windows Server 2003

The Department of Homeland Security (DHS) / Information Analysis and Infrastructure Protection (IAIP) National Cyber Security Division (NCSD) is issuing this advisory in consultation with the Microsoft Corporation to heighten awareness of potential Internet disruptions resulting from the possible spread of malicious software exploiting a vulnerability in popular Microsoft Windows operating systems.

DHS expects that exploits are being developed for malicious use. Two additional factors are causing heightened interest in this situation: the affected operating systems are in wide spread use, and exploitation of the vulnerability could permit the execution of arbitrary code. DHS and Microsoft are concerned that a properly written exploit could rapidly spread on the Internet as a worm or virus in a fashion similar to Code Red or Slammer.

The recently announced Remote Procedure Call (RPC) vulnerability in computers running Microsoft Windows operating systems listed above could be exploited to allow the execution of arbitrary code or could cause a denial of service state in an unprotected computer. Because of the significant percentage of Internet-connected computers running Windows operating systems and using high speed connections (DSL or cable for example), the potential exists for a worm or virus to propagate rapidly across the Internet carrying payloads that might exploit other known vulnerabilities in switching devices, routers, or servers.

There is a vulnerability in the part of RPC that deals with message exchange over TCP/IP. The vulnerability results from the handling of malformed messages. This particular vulnerability affects a Distributed Component Object Model (DCOM) interface with RPC, which listens on RPC enabled ports. This interface handles DCOM object activation requests that are sent by client machines (such as Universal Naming Convention (UNC) paths) to the server. An attacker who successfully exploited this vulnerability would be able to run code with local system privileges on an affected system. The attacker would be able to take any action on the system, including installing programs, viewing changing or deleting data, or creating new accounts with full privileges.

Due to the seriousness of the RPC vulnerability, DHS and Microsoft encourage system administrators and computer owners to take this opportunity to update vulnerable versions of Microsoft Windows operating systems as soon as possible. Microsoft updates, workarounds, and additional information are available at http://microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS03-026.asp

DHS and Microsoft further suggest that Internet Service Providers and network administrators consider blocking TCP and UDP ports 135, 139, and 445 for inbound connections unless absolutely needed for business or operational purposes.

Advisories recommend the immediate implementation of protective actions, including best practices when available. DHS encourages recipients of this advisory to report information concerning suspicious or criminal activity to law enforcement or a DHS watch office. The DHS Information Analysis and Infrastructure Protection watch offices may be contacted at:

For private citizens and companies - Phone: (202) 323-3205, 1-888-585-9078,
Email: nipc.watch@fbi.gov;
Online: http://www.nipc.gov/incident/cirr.htm
For telecommunications industry - Phone: (703) 607-4950
Email: ncs@dhs.gov
For Federal agencies/departments - Phone: (888) 282-0870
Email: fedcirc@fedcirc.gov
Online: https://incidentreport.fedcirc.gov

DHS intends to update this alert should it receive additional relevant information, including information provided to it by the user community. Based on this notification, no change to the Homeland Security Advisory System (HSAS) is anticipated; the current HSAS level is YELLOW.