php - Is it secure to submit forms this way?

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I am using PHP to submit forms on my website. When the action or logic is in another file, I do it this way:

<form action="<?php echo ROUTE; ?>/group.php?GI=<?php echo $group['ID']; ?>">

The constant ROUTE is being used to show the root folder, which is something like http://localhost/example/project. And the variable $group and the ID must be sent through the form so we can get this number on group.php.

My question is, is it secure to send the information this way or should I apply some kind of filters?