Dreambox DM500 webserver long URL request denial of service scip AG Vulnerability ID 3807 (08/29/2008) http://www.scip.ch/cgi-bin/smss/showadvf.pl?id=3807 I. INTRODUCTION Dreambox is a Linux-based DVB satellite, terrestrial and cable digital television decoder (set-top box), produced by German multimedia vendor Dream Multimedia. More information is available at the official product web site at the following URL: http://www.dream-multimedia-tv.de/ II. DESCRIPTION Marc Ruef at scip AG found an input validation error within the web interface of the model DM500C. Other models, for example DM500S, might be affected too. An attacker is able to send a very long http request string (approx. 512 bytes) to the web server which will cause a denial of service. The web interface and some parts of the operating system might not be responsible anymore. III. EXPLOITATION It is possible to exploit the vulnerability with a common web browser by using a long url. The http web server fingerprinting suite httprecon[1] is able to reproduce the problem too. Just use the test plugin get_long (activated by default). The Attack Tool Kit (ATK)[2] is able to exploit this vulnerability with the following generic ASL code (expand the long URL request): open|send GET http://192.168.0.1/aaa(...) HTTP/1.0\n\n|sleep|close|pattern_not_exists HTTP/1.# ### * IV. IMPACT Because the attack is possible without further authentication, users with access possibilities to the web server might affect the behavior of the device. The web interface and some parts of the operating system are not responsible anymore. A restart of the device is required to provide full functionality again. V. DETECTION Detection of web based attacks requires a specialized web proxy and/or intrusion detection system. Patterns for such a detection are available and easy to implement. VI. SOLUTION We have informed Dream Multimedia on an early stage. Our technical requests were not answered nor confirmed. Therefore, not official statement, patch or upgrade is available. We suggest to close the web interface in insecure environments. Especially the access via Internet should be prevented with restrictive configuation settings or an additional firewall device. VII. VENDOR RESPONSE Dream Multimedia has been informed first at 04/30/2008 via email to support-at-Dream-Multimedia-Tv.de. This message has been added to the ticketing system at http://tickets.dream-multimedia-tv.de. The same day it was assured to verify the mentioned condition. No further response came back. Other requests remained unanswered too. VIII. SOURCES scip AG - Security Consulting Information Process (german) http://www.scip.ch/ scip AG Vulnerability Database (german) http://www.scip.ch/cgi-bin/smss/showadvf.pl?id=3807 computec.ch document data base (german) http://www.computec.ch/download.php IX. DISCLOSURE TIMELINE 2008/04/28 Identification of the vulnerability by Marc Ruef 2008/04/30 First information to support-at-Dream-Multimedia-Tv.de 2008/04/30 Automated reply by the ticketing system (ticket id 2008043010000466) 2008/04/30 Manual response by Nils Weiberg announcing further investigation 2008/05/22 Request for current state of investigation 2008/05/22 Another response by Nils Weiberg that the research is ongoing 2008/07/15 Last request for current state of investigation 2008/07/15 Another response by Nils Weiberg without further details 2008/08/29 Public disclosure of the advisory X. CREDITS The vulnerability was discovered by Marc Ruef. Marc Ruef, scip AG, Zuerich, Switzerland maru-at-scip.ch http://www.scip.ch/ A1. BIBLIOGRAPHY [1] http://www.computec.ch/projekte/httprecon/ [2] http://www.computec.ch/projekte/atk/ A2. LEGAL NOTICES Copyright (c) 2007-2008 scip AG, Switzerland. Permission is granted for the re-distribution of this alert. It may not be edited in any way without permission of scip AG. The information in the advisory is believed to be accurate at the time of publishing based on currently available information. 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 from use of or reliance on this advisory.