The core flaw in v3.1 resides in the validate_email() function and the subsequent send_email() implementation. The script attempts to strip \r , \n , %0a , and %0d to prevent CRLF injection. However, due to a failure in recursive sanitization, attackers can double-encode or use alternative line feeds.
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) die("Invalid email format"); php email form validation - v3.1 exploit
If you run v3.1, assume compromise. Rotate all secrets, audit your mail logs, and rewrite your contact form using modern, maintained libraries. Version 3.1 belongs in the trash—not on your server. The core flaw in v3
victim@example.com\r\nBcc: target1@spam.com, target2@spam.com victim@example
// Vulnerable snippet from EmailValidator v3.1 public function sanitize_input($data) $data = trim($data); $data = stripslashes($data); $data = htmlspecialchars($data); // The fatal line: Only runs once, non-recursive $data = str_replace(array("\r", "\n", "%0a", "%0d"), '', $data); return $data;
The exploit typically targets the interaction between PHP and the underlying mail transfer agent (MTA), such as . Attack Vector Command Injection
Injecting -oQ/tmp/ -X/var/www/html/shell.php into the email field. Full server compromise via remote shell access.
