ECHU.ORG Alert #4: GuppY makes XSS attacks easy
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| GuppY makes XSS attacks easy |
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PROGRAM: GuppY
VULNERABLE VERSIONS: All versions under 2.4p1
IMMUNE VERSIONS: 2.4p1
SEVERITY: high
Tested version
==============
GuppY 2.4 on the official GuppY website.
Description
============
"GuppY is a small web portal, meant to be easy to use for the end user that you
are, and which does not require a database to run.This architecture allows then
to install it on almost all Internet web sites hosters (or almost all of them),
the only preriquisite being that your hoster has to provide the PHP scripting
language facility." - GuppY website
GuppY use the postguest.php file for its forum and guestbook modules. This file
contain XSS holes, an attacker can execute code since [c=codecolor]text[/c] has
no filter.
POSTGUEST.PHP
=============
Problems come from this part:
Line 196: $ptxt = preg_replace("/(\[c=(.*?)\])(.*?)(\[\/c\])/i", "<font
style=\"color:\\2\">\\3</font>",$ptxt);
Line 197: $ptxt = preg_replace("/(\[c=(.*?)\])(.*?)(\[\/C\])/i", "<font
style=\"color:\\2\">\\3</font>",$ptxt);
Line 198: $ptxt = preg_replace("/(\[C=(.*?)\])(.*?)(\[\/c\])/i", "<font
style=\"color:\\2\">\\3</font>",$ptxt);
Line 199: $ptxt = preg_replace("/(\[C=(.*?)\])(.*?)(\[\/C\])/i", "<font
style=\"color:\\2\">\\3</font>",$ptxt);
A badly disposed member can post a message containing code really easily in
forum and guestbook modules. Example:
(This proof-of-concept will show a window that can freeze your computer if
using Internet Explorer so take care)
[c=expression(alert('unsecure'))]texte[/c]
Solution
========
In order to avoid the vulnerability, add a filter that will block ;<>*()"']
caracters to lines 196 to 199:
Line 196: $ptxt = preg_replace("/(\[c=([#a-zA-Z0-9]*)\])(.*?)(\[\/c\])/i",
"<font style=\"color:\\2\">\\3</font>",$ptxt);
Line 197: $ptxt = preg_replace("/(\[c=([#a-zA-Z0-9]*)\])(.*?)(\[\/C\])/i",
"<font style=\"color:\\2\">\\3</font>",$ptxt);
Line 198: $ptxt = preg_replace("/(\[C=([#a-zA-Z0-9]*)\])(.*?)(\[\/c\])/i",
"<font style=\"color:\\2\">\\3</font>",$ptxt);
Line 199: $ptxt = preg_replace("/(\[C=([#a-zA-Z0-9]*)\])(.*?)(\[\/C\])/i",
"<font style=\"color:\\2\">\\3</font>",$ptxt);
Vendor status
==============
GuppY developper's team has been contacted, a patch has been released tonight
that fix the problem. Thanks to aldweb (freeguppy.org webmaster) for his quick
answer.
Links
=====
GuppY: http://www.freeguppy.org
Patch: http://www.freeguppy.org/file/guppy_patch2.zip
Version 2.4p1: http://www.freeguppy.org/file/guppy.zip
This vulnerability's orginal paper can be found here:
http://www.echu.org/articles/alertes/echu-alert4.txt
David Suzanne (dAs)
das[a]echu.org
http://www.echu.org
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