Reported by:
SEC Consult Vulnerability Lab / www.sec-consult.com

Vulnerability overview:

Due to unchecked user input, arbitrary files can be included within a PHP require_once() statement. Input length is limited to 32 characters. This vulnerability allows for reading arbitrary files on the affected webserver, as well as code execution if the attacker can put php code in any includable file (which is possible in most scenarios).

Vulnerability description:

Vulnerable files/objects: core/lang_api.php, account_prefs_update.php

Line 37 (in "core/lang_api.php") loads text file with user-supplied language preference.

---cut here---
require_once( $t_langdir . 'strings' . $p_lang . '.txt' );
---cut here---

Proof of concept:

Use account_prefs_update.php to set language to something like:

language=urdu.txt/../../../../etc/passwd%00