[UNIX] YaBB Cross-Site Scripting Vulnerability (NULL)

From: support@securiteam.com
Date: 06/23/02


From: support@securiteam.com
To: list@securiteam.com
Date: Sun, 23 Jun 2002 21:42:07 +0200 (CEST)

The following security advisory is sent to the securiteam mailing list, and can be found at the SecuriTeam web site: http://www.securiteam.com
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  YaBB Cross-Site Scripting Vulnerability (NULL)
------------------------------------------------------------------------

SUMMARY

 <http://yabb.xnull.com/> YaBB is a leading provider of free, downloadable
Perl forums for webmasters. A security vulnerability in the product allows
a remote attacker to insert malicious HTML and JavaScript into web pages
presented to users.

DETAILS

Vulnerable systems:
 * YaBB 1 Gold SP1 and earlier versions

When accessing a thread that does not exist, YaBB will give an error about
the board not existing.
Example:
http://some.site.com/cgi-bin/YaBB/YaBB.cgi?board=BOARD&action=display&num=NULL

This will trigger an error in the CGI script and output the following:
This topic does not exist on this board. NULL : 96.

The problem here should be obvious. By constructing JavaScript code in
place of NULL, a malicious user can trick someone into running the code of
his or her choice, since YaBB does not filter user input/script output.

Exploit:
http://some.site.com/cgi-bin/YaBB/YaBB.cgi?board=BOARD&action=display&num=>alert()</script>

Vendor status:
Vendor was notified 05/14/02.

ADDITIONAL INFORMATION

The information has been provided by
<mailto:
methodic@bigunz.angrypacket.com> methodic.

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