    public function urlOrExistingFilepath($fields)
    {
        if ($this->isFeedLocal($this->data)) {
            $path = mb_ereg_replace("/\:\/\//", '', $this->data['Feed']['url']);
            if ($this->data['Feed']['source_format'] == 'misp') {
                if (!is_dir($path)) {
                    return 'For MISP type local feeds, please specify the containing directory.';
                }
            } else {
                if (!file_exists($path)) {
                    return 'Invalid path or file not found. Make sure that the path points to an existing file that is readable and watch out for typos.';
                }
            }
        } else {
            if (!filter_var($this->data['Feed']['url'], FILTER_VALIDATE_URL)) {
                return false;
            }
        }
        return true;
    }
The application deserializes untrusted data without sufficiently verifying that the resulting data will be valid.