source: https://www.securityfocus.com/bid/24383/info

WordPress is prone to a cross-site scripting vulnerability because the application fails to properly sanitize user-supplied input.

An attacker may leverage this issue to execute arbitrary script code in the browser of an unsuspecting user. This may help the attacker steal cookie-based authentication credentials and launch other attacks.

WordPress 2.2. is vulnerable; other versions may also be affected. 

http://www.example.com/wp-admin/themes.php?page=functions.php&zmx"><script>alert(1)</script>