YaBB Forum member.vars CRLF Injection Privilege Escalation Vulnerability iDefense Security Advisory 06.12.07 http://labs.idefense.com/intelligence/vulnerabilities/ Jun 12, 2007 I. BACKGROUND YaBB (Yet another Bulletin Board) is an Open Source community forum system written in Perl. More information is available at the following URL. http://www.yabbforum.com/ II. DESCRIPTION Remote exploitation of an input validation error within version 2.1 of YaBB Forum allows attackers to register with forum Administrator privileges. The problem specifically exists due to insufficient validation when writing to the "vars" file for each user. By setting the values of certain variables to contain certain characters, attackers can elevate their privileges to that of the forum Administrator. III. ANALYSIS Exploitation allows attackers to obtain Administrator privileges, which include the ability to modify forum templates (i.e., Perl code). This allows administrators to execute arbitrary commands in the context of the web server running the forum. This attack can be performed during registration. This allows unauthenticated attackers to obtain forum Administrator privileges at registration time via the register.pl script. Additionally, once registered, a forum user can modify their profile and conduct this attack using the profile.pl script. IV. DETECTION iDefense confirmed the existence of this vulnerability within version 2.1 of YaBB Forum. V. WORKAROUND Disabling the registration feature of the forum mitigates this issue. VI. VENDOR RESPONSE The YaBB Forum team has addressed this vulnerability by releasing a software update. For more information consult the following announce on their home site. http://www.yabbforum.com/community/?board=general;action=display;num=1181678785 VII. CVE INFORMATION A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet. VIII. DISCLOSURE TIMELINE 05/23/2007 Initial vendor notification 05/23/2007 Initial vendor response 06/12/2007 Coordinated public disclosure IX. CREDIT This vulnerability was reported to iDefense by Peter Vreugdenhil. Get paid for vulnerability research http://labs.idefense.com/methodology/vulnerability/vcp.php Free tools, research and upcoming events http://labs.idefense.com/ X. LEGAL NOTICES Copyright © 2007 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 e-mail 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. _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/