HTML Form found in redirect page

Description

Manual confirmation is required for this alert.

An HTML form was found in the response body of this page. However, the current page redirects the visitor to another page by returning an HTTP status code of 301/302. Therefore, all browser users will not see the contents of this page and will not be able to interact with the HTML form.

Sometimes programmers don't properly terminate the script after redirecting the user to another page. For example:
<?php
    if (!isset($_SESSION["authenticated"])) {
        header("Location: auth.php");
    }
?>
<title>Administration page</title>
<form action="/admin/action" method="post">
    <!-- ...  form inputs ...  -->
</form>
  
<!-- ...  the rest of the administration page ...  -->
This script is incorrect because the script is not terminated after the "header("Location: auth.php");" line. An attacker can access the content the administration page by using an HTTP client that doesn't follow redirection (like HTTP Editor). This creates an authentication bypass vulnerability.
The correct code would be

<?php
    if (!isset($_SESSION[auth])) {
        header("Location: auth.php");
        exit();
    }
?>
<title>Administration page</title>
<form action="/admin/action" method="post">
    <!-- ...  form inputs ...  -->
</form>
    
<!-- ...  the rest of the administration page ...  -->

Remediation

Make sure the script is terminated after redirecting the user to another page.

References