Public Vulnerability Reports

YaBB Forum member.vars CRLF Injection Privilege Escalation Vulnerability



YaBB (Yet another Bulletin Board) is an Open Source community forum system written in Perl. More information is available at the following URL.


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.


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 script.

Additionally, once registered, a forum user can modify their profile and conduct this attack using the script.


iDefense confirmed the existence of this vulnerability within version 2.1 of YaBB Forum.


Disabling the registration feature of the forum mitigates this issue.


The YaBB Forum team has addressed this vulnerability by releasing a software update. For more information consult the following announce on their home site.;action=display;num=1181678785


A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet.


05/23/2007 Initial vendor notification
05/23/2007 Initial vendor response
06/12/2007 Coordinated public disclosure


This vulnerability was reported to iDefense by Peter Vreugdenhil.

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