When someone uploads a file which is greater than the max upload limit set in php.ini, the user is shown a message saying "A required parameter(sesskey) was missing" instead of the actual factor.

I noticed this error, while trying to restore a backup.

The code responsible for the correct message is (repository_ajax.php)

// If uploaded file is larger than post_max_size (php.ini) setting, $_POST content will be empty.

if (empty($_POST) && !empty($action)) {

    $err->error = get_string('errorpostmaxsize', 'repository');

    die(json_encode($err));

}

Seems it is expecting $_GET['action'] to be set, which is not in this case.

I have not tested in other places to be sure if the problem is localized to the restore page or not.