YCCMS 3.4 未授权更改管理员账号密码

public function update(){
if(isset($_POST['send'])){
if(validate::isNullString($_POST['username'])) Tool::t_back('用户名不能为空','?a=admin&m=update');
if(validate::isNullString($_POST['password'])) Tool::t_back('密码不能为空!','?a=admin&m=update');
if(!(validate::checkStrEquals($_POST['password'], $_POST['notpassword']))) Tool::t_back('两次密码不一致!','?a=admin&m=update');
$this->_model->username=$_POST['username'];
$this->_model->password=sha1($_POST['password']);
$_edit=$this->_model->editAdmin();
if($_edit){
tool::layer_alert('密码修改成功!','?a=admin&m=update',6);
}else{
tool::layer_alert('密码未修改!','?a=admin&m=update',6);
}
}

$this->_tpl->assign('admin', $_SESSION['admin']);
$this->_tpl->display('admin/public/update.tpl');
}

public function editAdmin(){
$_sql="UPDATE
my_admin
SET
username='$this->username',
password='$this->password'
WHERE
id=1
LIMIT 1";
return parent::update($_sql);
}

protected function update($_sql){
return $this->execute($_sql)->rowCount();
}

protected function execute($_sql){
try{
$_stmt=$this->_db->prepare($_sql);
$_stmt->execute();
}catch (PDOException $e){
exit('SQL语句:'.$_sql.'<br />错误信息:'.$e->getMessage());
}
return $_stmt;
}
}