The vulnerability in PHP email validation version 3.1 allows an attacker to bypass standard input filters to achieve Remote Code Execution (RCE) or Email Header Injection . This occurs when the script fails to sanitize the "Sender" or "From" fields before passing them to internal mail functions like mail() or libraries like PHPMailer. How the Exploit Works
<?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"; php email form validation - v3.1 exploit
Instead of a standard email address, an attacker might submit: attacker@example.com%0ACc:spam-target@domain.com 2. The Vulnerable Code A typical vulnerable PHP snippet looks like this: The vulnerability in PHP email validation version 3
An attacker inserts newline characters ( \r\n or %0A%0D ) into a form field like "Subject" or "Name". The Vulnerable Code A typical vulnerable PHP snippet
By putting a PHP shell (e.g., ) in the body of the email, the log file becomes an executable web shell. 3. Vulnerability Indicators
To secure forms, always follow the rule (Filter Input, Escape Output) :