CERT Advisory CA-2003-19 Exploitation of Vulnerabilities in Microsoft RPC Interface

From: CERT Advisory (cert-advisory_at_cert.org)
Date: 07/31/03


Date: Thu, 31 Jul 2003 16:58:29 -0400
To: cert-advisory@cert.org


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CERT Advisory CA-2003-19 Exploitation of Vulnerabilities in Microsoft RPC
Interface

   Original issue date: July 31, 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 NT 4.0 Terminal Services Edition
     * Microsoft Windows 2000
     * Microsoft Windows XP
     * Microsoft Windows Server 2003

Overview

   The CERT/CC is receiving reports of widespread scanning and
   exploitation of two recently discovered vulnerabilities in Microsoft
   Remote Procedure Call (RPC) Interface.

I. Description

   Reports to the CERT/CC indicate that intruders are actively scanning
   for and exploiting a vulnerability in Microsoft's DCOM RPC interface
   as described in VU#568148 and CA-2003-16. Multiple exploits for this
   vulnerability have been publicly released, and there is active
   development of improved and automated exploit tools for this
   vulnerability. Known exploits target TCP port 135 and create a
   privileged backdoor command shell on successfully compromised hosts.
   Some versions of the exploit use TCP port 4444 for the backdoor, and
   other versions use a TCP port number specified by the intruder at
   run-time. We have also received reports of scanning activity for
   common backdoor ports such as 4444/TCP. In some cases, due to the RPC
   service terminating, a compromised system may reboot after the
   backdoor is accessed by an intruder.

   There appears to be a separate denial-of-service vulnerability in
   Microsoft's RPC interface that is also being targeted. Based on
   current information, we believe this vulnerability is separate and
   independent from the RPC vulnerability addressed in MS03-026. The
   CERT/CC is tracking this additional vulnerability as VU#326746 and is
   continuing to work to understand the issue and mitigation strategies.
   Exploit code for this vulnerability has been publicly released and
   also targets TCP port 135.

   In both of the attacks described above, 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.

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.

Filter network traffic

   Sites are encouraged to block network access to the RPC service 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
     * 135/TCP
     * 135/UDP
     * 139/TCP
     * 139/UDP
     * 445/TCP
     * 445/UDP

   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 exploitation of the first
   vulnerability (VU#568148) as CERT#27479 and the second vulnerability
   (VU#326746) as CERT#24523. 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 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
   ______________________________________________________________________

   Authors: Chad Dougherty and Kevin Houle
   ______________________________________________________________________

   This document is available from:
   http://www.cert.org/advisories/CA-2003-19.html
   ______________________________________________________________________

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   Revision History

   July 31, 2003: Initial release

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