ISS Security Advisory -- MS Exchange 5.x

[jlarimer () ISS NET (Jon Larimer)]

ISS Security Advisory
July 24, 1998


Denial of Service attacks against Microsoft Exchange 5.0 to 5.5

Synopsis:

An attacker can disrupt an organization by crashing Microsoft Exchange
Server over the network.  This attack will stop e-mail and other services
that Exchange provides for the organization.

Recommended Action:

Install vendor supplied hotfixes for Microsoft Exchange 5.0, and 5.5.
Hotfixes are available for Exchange 5.0 and 5.5 at the following
locations:

Exchange Server 5.0 ALL LANGUAGES:
   ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/
   Eng/Exchg5.0/Post-SP2-STORE/
   ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/
   Eng/Exchg5.0/Post-SP2-IMS/

Exchange Server 5.5 ENGLISH:
   ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/
   Eng/Exchg5.5/PostRTM/STORE-FIX
   ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/
   Eng/Exchg5.5/PostRTM/IMS-FIX

Exchange Server 5.5 FRENCH:
   ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/
   Frn/Exchg5.5/PostRTM/STORE-FIX
   ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/
   Frn/Exchg5.5/PostRTM/IMS-FIX
Exchange Server 5.5 GERMAN:
   ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/
   Ger/Exchg5.5/PostRTM/STORE-FIX
   ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/
   Ger/Exchg5.5/PostRTM/IMS-FIX

Exchange Server 5.5 JAPANESE:
   ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/
   Jpn/Exchg5.5/PostRTM/STORE-FIX
   ftp://ftp.microsoft.com/bussys/exchange/exchange-public/fixes/
   Jpn/Exchg5.5/PostRTM/IMS-FIX

If you cannot apply the hotfix immediately, Microsoft recommends that you
configure the Server Monitor in Microsoft Exchange Server Administrator to
automatically restart the affected services if they stop.

Determining if you are vulnerable:
If you are running Microsoft Exchange 5.0 or 5.5 without appropriate
hotfixes,
you are vulnerable to the attacks.

Description:

There are vulnerabilities in the Exchange Internet Mail Service (IMS), the
service that handles the SMTP protocol, and the Information Store, the
service that handles the NNTP protocol, that will allow an attacker to
crash the Internet Mail Service or the Information Store. These
vulnerabilities are related to the way that the IMS handles the AUTH
command and how the Information Store's NNTP server handles AUTHINFO. Both
of these systems experience buffer overflow issues.

A similar problem not related to the buffer overflow issue involves how
IMS
handles the AUTH command. This issue will also cause the service to crash.

Note that when the Internet Mail Service crashes, the rest of Microsoft
Exchange will still operate. When the Information Store crashes, Exchange
Server cannot operate.

Vulnerable Versions:

Microsoft Exchange Server 5.0 and 5.5 are vulnerable without hotfixes
applied

Additional Information:

There are two Microsoft Knowledge Base articles that address these issues
-- Q188369 and Q188341. These can be obtained from Microsoft Support
Online
at http://support.microsoft.com. ISS X-Force thanks the Microsoft Exchange
group for providing assistance and patches to these issues in a timely
fashion.

These security issues were discovered by Jon Larimer of ISS X-Force
<jlarimer () iss net>.


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Copyright (c) 1998 by Internet Security Systems, Inc.

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The information within this paper may change without notice. Use of this
information constitutes acceptance for use in an AS IS condition. There
are
NO warranties with regard to this information. In no event shall the
author
be liable for any damages whatsoever arising out of or in connection with
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Please send suggestions, updates, and comments to:
X-Force <xforce () iss net> of Internet Security Systems, Inc.


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