Php Email Form Validation - V3.1 Exploit -

Attackers know that this regex allows newlines ( %0a ), carriage returns ( %0d ), and certain special characters inside the local part if URL-encoded. By submitting:

filter_var($email, FILTER_VALIDATE_EMAIL) While FILTER_VALIDATE_EMAIL is better, it prevent header injection. An email like "attacker\r\nBcc: spam"@example.com passes validation but still contains CRLF characters after decoding in some PHP edge cases (especially with multibyte strings). php email form validation - v3.1 exploit

email = "shell.php%00.jpg" Due to PHP's old %00 (null byte) injection (fixed in PHP 5.3.4+ but still present on outdated hosts), the file becomes logs/shell.php . Then, they inject PHP code via the message field: Attackers know that this regex allows newlines (

// Additional header injection cleanup $email = str_replace(array("\r", "\n", "%0a", "%0d"), '', $email); If you must, use mb_encode_mimeheader() or a safe wrapper. Step 4: Disallow null bytes and control characters. if (preg_match('/[\x00-\x1F\x7F]/', $input)) http_response_code(400); exit("Invalid characters"); email = "shell

Vulnerable v3.1 code example:

As of my current knowledge base (up to May 2025), there is no widely documented, specific CVE (Common Vulnerabilities and Exposures) titled exactly "PHP Email Form Validation - v3.1 Exploit." However, this article will treat this as a case study of a legacy library version (3.1) that contains a chained exploit —combining validation bypass and Remote Code Execution (RCE)/Email Header Injection. This pattern is extremely common in outdated PHP scripts. The Anatomy of the "PHP Email Form Validation - v3.1 Exploit": How Attackers Bypass Sanitization and Own Your Server Introduction: The Silent Killer of Contact Forms For two decades, the PHP contact form has been the gateway between a business and its customers. But in the shadows of legacy code, a specific vulnerability chain known colloquially as the "v3.1 Exploit" is actively being weaponized.