Microsoft Distributed Transaction Controller Packet Relay DoS
Vulnerability

iDEFENSE Security Advisory 10.11.05
www.idefense.com/application/poi/display?id=319&type=vulnerabilities
October 11, 2005

I. BACKGROUND

The Distributed Transaction Controller provides a method for disparate 
processes to complete atomic transactions. The Transaction Internet 
Protocol (TIP) is one the ways that the DTC service can be accessed.
This service is part of a standard installation on Windows NT 4.0,
Windows 2000, Windows XP and Windows 2003.

II. DESCRIPTION

Remote exploitation of a denial of service vulnerability within various
versions of Microsoft Corp.'s Windows operating system allows attackers
to flood systems with connection attempts from legitimate MSDTC
servers.

The vulnerability specifically exists because of the functionality in
the TIP protocol that allows a remote IP address and port number to be
specified for a connection. The attack can be performed by connecting
to the MSDTC server and providing an identifier that contains the IP 
address and port number to flood. After a specific sequence of commands,
the attacker can force an error and cause the DTC service to connect to
the target IP and port. The DTC service will continue to make
connections to that host and port, one at a time, per stalled
transaction.

If the target host and port provides anything other than a certain set
of response messages to the IDENTIFY request on the connection, the DTC
service will disconnect and then reconnect to the service. The attacker
can keep submitting new transactions to the DTC service, increasing the 
total number of connections made to the target.

III. ANALYSIS

Successful exploitation of this vulnerability could allow an attacker to
proxy a denial of service attack through a MSDTC server that they do
not otherwise have access to. An attacker could easily scan public IP
ranges and find servers with TIP enabled and then force them to flood a
target with repeated connections attempts.

This attack can also be used to cause a DoS on the MSDTC server itself
by specifying a loopback address with port 445. This service should not
be exposed to public networks, thus mitigating the risk of this
vulnerability.

IV. DETECTION

iDEFENSE has confirmed the existence and exploitability of this 
vulnerability in Microsoft Windows 2000 SP4. All versions of Microsoft 
Windows with the vulnerable service running are suspected vulnerable.

V. WORKAROUND

iDEFENSE is currently unaware of any workarounds for this issue.

VI. VENDOR RESPONSE

The vendor security advisory and appropriate patches are available at:

   http://www.microsoft.com/technet/security/Bulletin/MS05-051.mspx

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2005-1980 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

03/23/2005 Initial vendor notification
03/23/2005 Initial vendor response
10/11/2005 Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.