This website uses cookies to distinguish you from other users of our website. The use of cookies helps us to provide you with a specific service, to facilitate website use, to understand our visitors and to advertise to you. By continuing to browse the site you are giving consent to our use of cookies. Learn more in our Privacy Statement.

Security Services

RealNetworks RealPlayer 11 HTTP Chunked Encoding Integer Overflow Vulnerability



RealPlayer is an application for playing various media formats, developed by RealNetworks Inc. Since late 2003, Real Player has been based on the open-source Helix Player. More information can be found at the URLs shown. For more information, see the vendor's site found at the following link.


Remote exploitation of an integer overflow vulnerability in RealNetworks Inc.'s RealPlayer 11 could allow an attacker to execute arbitrary code with the privileges of the affected service.

The vulnerability specifically exists in the handling of the 'chunked' Transfer-Encoding method. This method breaks the file the server is sending into 'chunks'. For each chunk, the server first sends the length of the chunk in hexadecimal, followed by the chunk data. This is repeated until there are no more chunks. The server then sends a chunk length of zero (0) indicating the end of the transfer. When processing these chunks, an integer overflow occurs, which results in a heap overflow. This leads to the execution of arbitrary code.


Exploitation of this vulnerability results in the execution of arbitrary code with the privileges of the user executing Real Player.

To be successful, an attacker must persuade a user to use Real Player to view specially crafted media. This could be accomplished via a Web page using the RealPlayer plug-in or a direct link to the malicious media.

It appears that the RealPlayer plug-in for Firefox uses the browser to download files via HTTP. The RealPlayer chunked encoding processing is not used in this scenario. However, RealPlayer does provide a right-click context menu to open the document within RealPlayer itself. As such, using Firefox does not prevent exploitation altogether.


iDefense has confirmed the existence of this vulnerability in RealPlayer version 11 on Windows. A nightly build of RealPlayer for Linux was also confirmed to be vulnerable. Previous versions do not appear be affected.


iDefense is currently unaware of any workarounds for this issue.


RealNetworks has released a patch which addresses this issue. Information about downloadable vendor updates can be found by clicking on the URLs shown.


The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2009-4243 to this issue. This is a candidate for inclusion in the CVE list (, which standardizes names for security problems.


01/11/2008 Initial Contact
01/11/2009 Initial Response
02/01/2010 Coordinated public disclosure.


The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research

Free tools, research and upcoming events


Copyright © 2010 Verisign, 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 e-mail customer service 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.