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Internet Security Systems Security Advisory
November 12, 2001

Multi-Vendor Buffer Overflow Vulnerability in CDE Subprocess Control Service

Synopsis:

Internet Security Systems (ISS) X-Force has discovered a buffer overflow
in the Subprocess Control Server (dtspcd) in all Unix variants running
CDE (Common Desktop Environment) system. The vulnerability in the dtspcd
daemon may allow remote attackers to execute arbitrary commands on a 
target system with super user privilege.

Affected Versions:

Many Unix vendors are affected by this vulnerability. 

ISS X-Force has been working with CERT on this issue. Please refer
to the CERT advisory at the following address for the current list
of vulnerable versions:
http://www.cert.org/advisories/CA-2001-31.html

Description:

CDE is the default X-Windows GUI environment shipped with newer versions
of Sun Solaris and many other Unix variants. The Subprocess Control
Server daemon is not intended to be run by normal users and is spawned
by other components within the CDE system. Dtspcd is started by the
Internet services daemon (inetd) when a CDE client attempts to create a
process on the daemon’s host.

A buffer overflow condition exists in the connection negotiation routine
within dtpscd. A remote attacker can generate a specially crafted CDE
client request to take advantage of the flaw and overflow exploit code
onto the heap. The attacker can use this exploit code to execute
arbitrary commands on the target system.

The Subprocess Control Server daemon is enabled by default on all
operating systems with CDE installed. This process is run by the
"root" user and accepts remote connections by default.

Recommendations:

This advisory was tentatively scheduled for release in December 2001.
The issue was made public in the following announcement before most
vendors were able to make patches available:
ftp://stage.caldera.com/pub/security/openunix/CSSA-2001-SCO.30/

ISS X-Force encourages all affected users to check with your individual
vendors for patch availability. Users should take steps to disable or
limit access to the vulnerable service until patches are made available.

ISS RealSecure Network Sensor customers can configure a Connection Event
for port 6112 to detect potential attacks. For more information on
configuring Connection Events, refer to the RealSecure 6.0 Network
Sensor Policy Guide, or the RealSecure 5.x Network Sensor User Guide.

ISS RealSecure Server Sensor customers can configure Server Sensor to
block access attempts to the dtspc port. The following steps describe
how to add a Firecell rule to RealSecure Server Sensor (Solaris and
Linux) to block access attempts to the dtspc port. X-Force recommends
that administrators investigate the implications of blocking dtspc in
their environments before applying this rule.

1. Open the server sensor policy to which you want to add this signature.
2. Select the Protect tab, open the Protect folder, and then open the
   Firecell folder.
3. Select the TCP Inbound section.
4. Click Add to create a new signature.
5. Type a name for the firecell signature, e.g. Block_dtspcd, and then
   click OK.
   The new signature is added to the policy in the TCP Inbound section.
6. Select the signature that you just created.
   The properties of the signature appear in the right pane.
7. Set the priority of the event in the Priority box. 
8. In the Port number field, type 6112.
9. In the IP address field, select ANY ADDRESS.
10. In the Actions section, select Action (1) In the range of IP
    addresses, drop the packet and generate the responses.
11. In the Response section, select the responses you want the sensor
    to take when a match to this signature occurs.
12. Save and apply the policy to the sensor.


ISS X-Force will provide specific detection and assessment support for
this vulnerability in upcoming X-Press Updates for RealSecure Network
Sensor and Internet Scanner. ISS will also provide detection support in
an upcoming signature update for BlackICE products.

Additional Information:

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2001-0803 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

http://www.cert.org/advisories/CA-2001-31.html
http://www.kb.cert.org/vuls/id/172583
http://xforce.iss.net/static/7396.php

Credits:

This vulnerability was discovered and researched by Chris Spencer of the
ISS X-Force. Internet Security Systems would like to thank CERT for
their response and handling of this vulnerability. 

______

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 8,000 customers worldwide
including 21 of the 25 largest U.S. commercial banks and the top 10 U.S.
telecommunications companies. 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 www.iss.net or call 888-901-7477.

Copyright (c) 2001 Internet Security Systems, Inc. All rights reserved
worldwide.

Permission is hereby granted for the redistribution of this Alert
electronically. It is not to be edited in any way without express
consent of the X-Force. If you wish to reprint the whole or any part
of this Alert in any other medium excluding electronic medium, please
e-mail xforce@iss.net for permission.

Disclaimer

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: http://xforce.iss.net/sensitive.php
as well as on MIT's PGP key server and PGP.com's key server.

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


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