使用空字段（蜜罐）保护表单免受垃圾邮件（PHP）的侵害

Question

I have a simple contact form in a Wordpress website, that needs some protecting.

I gave it two empty fields named "website" and "email" and hid them with CSS (visibility: hidden;). So far, so good.

The problem now is, I just cannot give the PHP commands

if(isset($_POST['website'])) die();
if(isset($_POST['email'])) die();

the proper position in my PHP file. Can you tell me where to position it correctly?

Here is my PHP file:

<?php
if(isset($_POST['website'])) die();
if(isset($_POST['email'])) die();
if(isset($_POST['submitted'])) {

    if(trim($_POST['contactVorname']) === '') {
        $vornameError = '*';
        $hasError = true;
    } else {
        $vorname = trim($_POST['contactVorname']);
    }

    if(trim($_POST['contactName']) === '') {
        $nameError = '*';
        $hasError = true;
    } else {
        $name = trim($_POST['contactName']);
    }

    if(trim($_POST['contactEmail']) === '')  {
        $emailError = '*';
        $hasError = true;
    } else if (!preg_match("/^[[:alnum:]][a-z0-9_.-]*@[a-z0-9.-]+\.[a-z]{2,4}$/i", trim($_POST['contactEmail']))) {
        $emailError = '*';
        $hasError = true;
    } else {
        $email = trim($_POST['contactEmail']);
    }

    if(trim($_POST['unternehmen']) === '') {
/*      $unternehmenError = '*';
        $hasError = true; */
    } else {
        $unternehmen = trim($_POST['unternehmen']);
    }

    if(trim($_POST['ort']) === '') {
/*      $ortError = '*';
        $hasError = true; */
    } else {
        $ort = trim($_POST['ort']);
    }

    if(trim($_POST['telefon']) === '') {
/*      $telefonError = '*';
        $hasError = true; */
    } else {
        $telefon = trim($_POST['telefon']);
    }

    if(trim($_POST['betreff']) === '') {
        $betreffError = '*';
        $hasError = true;
    } else {
        $betreff = trim($_POST['betreff']);
    }

    if(trim($_POST['comments']) === '') {
        $commentError = '*';
        $hasError = true;
    } else {
        if(function_exists('stripslashes')) {
            $comments = stripslashes(trim($_POST['comments']));
        } else {
            $comments = trim($_POST['comments']);
        }
    }

    if(!isset($hasError)) {
        $emailTo = get_option('tz_email');
        if (!isset($emailTo) || ($emailTo == '') ){
            $emailTo = get_option('admin_email');
        }
        $subject = 'Kontaktformular | '.$vorname.' '.$name;
        $body = "\n.: Kontaktformular-E-Mail :. \n\nName: $vorname $name \nE-Mail: $email \n\nUnternehmen: $unternehmen \nOrt: $ort \nTelefon: $telefon \n\nBetreff: $betreff \n\nNachricht: $comments";
        $headers = 'From: '.$vorname.' '.$name.' <'.$emailTo.'>' . "\r\n" . 'Reply-To: ' . $email;

        wp_mail($emailTo, $subject, $body, $headers);
        $emailSent = true;
    }

}
?>

<?php get_header(); ?>

    <?php if (have_posts()) : while (have_posts()) : the_post(); ?>

        <article class="post" id="post-<?php the_ID(); ?>">

        <h2 class="gross"><?php the_title(); ?></h2>

        <div id="inhalt">

            <div class="seitebeitrag">

            <?php if(isset($emailSent) && $emailSent == true) { ?>
            <div><p>Vielen Dank für die Nachricht. Wir melden uns so schnell wie möglich zurück.</p></div>
            <?php } else { ?>

        <?php the_content(); ?>

            <form action="" id="contactForm" method="post">
            <div id="kf0">&nbsp;</div>
            <div id="kf1">
            <p><label for="contactVorname">Vorname *</label><br />
            <input type="text" name="contactVorname" id="contactVorname" value="<?php if(isset($_POST['contactVorname'])) echo $_POST['contactVorname'];?>" maxlength="50" />
            <?php if(!empty($vornameError)) { ?>
            <span class="fehler"><?=$vornameError;?></span>
            <?php } ?></p>

            <p><label for="contactName">Nachname *</label><br />
            <input type="text" name="contactName" id="contactName" value="<?php if(isset($_POST['contactName'])) echo $_POST['contactName'];?>" maxlength="50" />
            <?php if(!empty($nameError)) { ?>
            <span class="fehler"><?=$nameError;?></span>
            <?php } ?></p>

            <p><label for="contactEmail">E-Mail *</label><br />
            <input type="text" name="contactEmail" id="contactEmail" value="<?php if(isset($_POST['contactEmail']))  echo $_POST['contactEmail'];?>" maxlength="50" />
            <?php if(!empty($emailError)) { ?>
            <span class="fehler"><?=$emailError;?></span>
            <?php } ?></p>

            <p><label for="unternehmen">Unternehmen</label><br />
            <input type="text" name="unternehmen" id="unternehmen" value="" maxlength="50" /></p>

            <p><label for="ort">Ort</label><br />
            <input type="text" name="ort" id="ort" value="" maxlength="50" /></p>

            <p><label for="telefon">Telefon</label><br />
            <input type="text" name="telefon" id="telefon" value="" maxlength="50" /></p>

            <input type="text" id="website" name="website" value="" maxlength="80" /><br />
            <input type="text" id="email" name="email" value="" maxlength="80" />

            </div>

            <div id="kf2">
            <p><label for="betreff">Betreff *</label><br />
            <input type="text" name="betreff" id="betreff" value="<?php if(isset($_POST['betreff']))  echo $_POST['betreff'];?>" maxlength="50" />
            <?php if(!empty($betreffError)) { ?>
            <span class="fehler"><?=$betreffError;?></span>
            <?php } ?></p>      

            <p><label for="commentsText">Nachricht *</label><br />
            <textarea name="comments" id="commentsText" rows="20" cols="30"><?php if(isset($_POST['comments'])) { if(function_exists('stripslashes')) { echo stripslashes($_POST['comments']); } else { echo $_POST['comments']; } } ?></textarea>
            <?php if(!empty($commentError)) { ?>
            <span class="fehler"><?=$commentError;?></span>
            <?php } ?></p>
            <p>* Pflichtfelder</p>
            </div>

            <div id="kf3">
            <input type="submit" value="SENDEN" alt="senden" class="btn" /><br /><input type="hidden" name="submitted" id="submitted" value="true" />
            </div>

            <div id="kf4">
            <?php if(isset($hasError) || isset($captchaError)) { ?>
            <div><p class="error fehler">* ungültige oder fehlende Daten</p></div>
            <?php } ?></div>

            </form>
            <?php } ?>

                <?php wp_link_pages(array('before' => __('Pages: '), 'next_or_number' => 'number')); ?>

            </div>


            <?php // edit_post_link(__('Edit this entry.'), '<p>', '</p>'); ?>

        </article>

        <?php // comments_template(); ?>

        <?php endwhile; endif; ?>

 <?php // get_sidebar(); ?>

<?php get_footer(); ?>

Right now, the form gets totally blocked out, after sending the data, ALTHOUGH the two fields in question are NOT FILLED IN.

Answer 1

$_POST['website'] & $_POST['email'] will always be 'set'. An empty form field still sets the corresponding $_POST entry to an empty string ('') and will always be true to isset . Try using !empty .

if (!empty($_POST['website'])) die();
if (!empty($_POST['email'])) die();

See more here: http://php.net/manual/en/function.empty.php and with a bit more detail here: https://www.virendrachandak.com/techtalk/php-isset-vs-empty-vs-is_null/

Be careful using this approach with commonly named fields. They may be automatically filled in by a browser's auto-fill feature meaning you'll be getting false-positives and real users will end up on a blank screen.