RealNetworks Helix Server Content-Length Denial of Service Vulnerability

iDEFENSE Security Advisory 10.07.04:
www.idefense.com/application/poi/display?id=151&type=vulnerabilities
October 7, 2004

I. BACKGROUND

RealNetworks Helix Universal Server is a universal digital media
delivery platform with industry leading performance, integrated content
distribution and Web services support. More information is available at
http://www.realnetworks.com.

II. DESCRIPTION

Remote exploitation of a denial of service (DoS) vulnerability in
RealNetworks, Inc.'s Helix Server could allow an attacker to restart and
potentially disable the server.

The problem specifically exists in the handling of specially crafted
POST requests. Generating a request with the Content-Length header set
to -1 triggers an integer handling error resulting in mass utilization
of memory and CPU time.

III. ANALYSIS

Any unauthenticated remote attacker can exploit this vulnerability,
which causes the affected system to utilize mass amounts of memory and
CPU time. The system will no longer be able to process future requests.

The affected server must be restarted in order to resume normal
functionality.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in
RealNetworks Helix Server version 9.0.2 for Linux and version 9.0.3 for
Windows. It is suspected that earlier versions on both platforms are
vulnerable as well.

V. WORKAROUND

Usage of an inline application level filter can help mitigate risk of
exploitation by scanning for and filtering invalid Content-Length
parameters.

VI. VENDOR RESPONSE

"Customers are encouraged to upgrade their Server software to the latest
version, which contains a security patch."

RealNetworks has released binaries that guard against the described
vulnerability. The related advisory from RealNetworks is available at:

    http://service.real.com/help/faq/security/security100704.html

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2004-0774 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

07/01/2004   Initial vendor notification
07/01/2004   iDEFENSE clients notified
08/05/2004   Initial vendor response
10/07/2004   Coordinated public Disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp

X. LEGAL NOTICES

Copyright (c) 2004 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDEFENSE. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email customerservice@idefense.com for permission.

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.