directory.php in AJchat 0.10 allows remote attackers to bypass input validation and conduct SQL injection attacks via a numeric parameter with a value matching the s parameter's hash value, which prevents the associated $_GET["s"] variable from being unset.  NOTE: it could be argued that this vulnerability is due to a bug in the unset PHP command (CVE-2006-3017) and the proper fix should be in PHP; if so, then this should not be treated as a vulnerability in AJChat.