Remote IIS Index Server ISAPI Extension Buffer Overflow

	Internet Security Systems Security Alert
June 19, 2001
Remote IIS Index Server ISAPI Extension Buffer Overflow

ISS X-Force is aware of a serious vulnerability that can be used to
attack all recent versions of Microsoft Internet Information Server
(IIS). A flaw exists in ISAPI Index Server extension query processing
that may lead to Web page defacement and theft of sensitive or 
confidential information. In addition, this vulnerability can be used in
conjunction with other exploits to further compromise affected systems.  

Internet Services Application Programming Interface (ISAPI ) extensions 
allow for additional functionality to be added to IIS. The ISAPI Index
Server extension provides a hook to integrate Microsoft Index Server 
with IIS. The vulnerability is introduced during the IIS installation
process, when two Index Server Dynamic Link Library (DLL ) files are
installed. Index Server itself does not need to be installed for 
attackers to exploit this vulnerability because these DLL files are
mapped by IIS default installations.  

When a vulnerable IIS installation receives an Index Server ISAPI query,
IIS parses the query to determine which extension corresponds to the 
request. Once the query is mapped to the correct extension, the body of
the request is parsed. The vulnerability is caused by a lack of bounds
checking on the length of the Index Server ISAPI request. Two potential
attack scenarios exist. A Denial of Service (DoS) attack can be 
launched against IIS by sending a very long string to the Index Server
ISAPI extension. Additionally, an attacker may use an advanced exploit
to send a specially-crafted long request to execute arbitrary code on
the vulnerable system. The Index Server ISAPI extension runs under the
"System" security context. Any successful attack will run under this 
context and may lead to unrestricted access of the target machine and 
its contents.

Affected Versions:
Microsoft Windows NT version 4.0
	Running IIS 4.0
Microsoft Windows 2000 Professional, Server, Advanced Server and 
Datacenter Server
	Running IIS 5.0

Detailed exploit information has been released, and ISS X-Force urges
all administrators to download and apply the following patches made
available by Microsoft. 

For Microsoft Windows NT version 4.0:

For Microsoft Windows 2000 Professional, Server and Advanced Server:

For Microsoft Windows 2000 Datacenter Server:
Patches for Windows 2000 Datacenter Server are hardware-specific and 
available from the original equipment manufacturer.

For more information on this vulnerability please refer to the Microsoft
Security Bulletin at:

ISS RealSecure intrusion detection customers may use the following 
user-defined signature to detect access attempts to .ida files. Follow
the instructions below to apply the user-defined signature to your 

From the Sensor window:
1. Right-click on the sensor and select 'Properties'.
2. Choose a policy you want to use, and click 'Customize'.
3. Select the 'User Defined Events' tab.
4. Click 'Add' on the right hand side of the dialog box.
5. Create a User Defined Event.
6. Type in a name of the event, such as 'IDA file access attempt'.
7. In the 'Context' field for each event, select 'URL_Data'. 
   In the 'String' field, type the following string:
8. Click 'Save', and then 'Close'.
9. Click 'Apply to Sensor' or 'Apply to Engine', depending on the
   version of RealSecure you are using.

ISS Internet Scanner X-Press Update version 4.10 provides assessment
capability for this vulnerability. 

Internet Scanner X-Press Update version 4.10 will be available later
this week for download at the following URL:

The next X-Press Update for ISS RealSecure Network Sensor will contain a
signature to detect this vulnerability.

NetworkICE provides an update for BlackICE products to detect this 
vulnerability. ISS X-Force recommends that all BlackICE customers refer
to the following URL for information regarding the detection of this 

Additional Information:
The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2001-0500 to this issue. This is a candidate for inclusion in
the CVE list (, which standardizes names for 
security problems.

For additional information about this vulnerability, please reference:


About Internet Security Systems (ISS)
Internet Security Systems is a leading global provider of security
management solutions for the Internet, protecting digital assets and
ensuring safe and uninterrupted e-business. With its industry-leading
intrusion detection and vulnerability assessment, remote managed
security services, and strategic consulting and education offerings, ISS
is a trusted security provider to more than 9,000 customers worldwide
including 21 of the 25 largest U.S. commercial banks, the top 10 U.S.
telecommunications companies, and all major branches of the U.S. Federal
Government. Founded in 1994, ISS is headquartered in Atlanta, GA, with
additional offices throughout North America and international operations
in Asia, Australia, Europe, Latin America and the Middle East. For more
information, visit the Internet Security Systems web site at
or call 888-901-7477.

Copyright (c) 2002 Internet Security Systems, Inc. All rights reserved

Permission is hereby granted for the redistribution of this Alert
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of this Alert in any other medium excluding electronic medium, please
e-mail for permission.


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 the use or spread of this information. Any use of this
information is at the user's own risk.

X-Force PGP Key available at: sensitive.php as
well as on MIT's PGP key server and's key server.

Please send suggestions, updates, and comments to: X-Force of Internet Security Systems, Inc.