403 Forbidden when passing a URL in a GET variable

I have this problem:
403 Forbidden on a PHP page with a URL encoded in the $ _GET parameter

I get the error "403 is forbidden" When I pass url as a GET variable like this

http://script/test.php?url=https://stackoverflow.com/questions/ask

But it normal.

http://script/test.php?url=stackoverflow.com/questions/ask

And even if I urlencode the url, it still gives me 403.

Apache mod_fcgid / 2.3.6 mod_auth_passthrough / 2.1 mod_bwlimited / 1.4 FrontPage / 5.0.2.2635 Server in ----- Port 80

And I don’t think mod_security is enabled on this server, because when I add SecFilterEngine Offto htaccess, I get "500 Internal Server Error".

Code snippet:

$URL = mysql_real_escape_string($_GET['url']);
mysql_query("INSERT INTO `url` ...");

So the question is, can I fix this without editing httpd.conf, because I do not have root privileges. thank