source: https://www.securityfocus.com/bid/19446/info

XennoBB is prone to a directory-traversal vulnerability because it fails to properly sanitize user-supplied input. 

An attacker can exploit this vulnerability to retrieve arbitrary files from the vulnerable system in the context of the affected application. Information obtained may aid in further attacks.

XennoBB 2.1.0 and earlier are vulnerable to this issue; other versions may also be affected.

http://www.example.com/profile.php?action=avatar_gallery&id={your registered user ID here}/category=../../general/