The server interprets the %0A as a line break, creating a new header line. The mail server now sees a valid Cc or Bcc instruction, sending the message to thousands of unauthorized recipients using your server's reputation. Beyond Spam: Escalating to RCE
Always validate email formats using filter_var($email, FILTER_VALIDATE_EMAIL) . 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 server interprets the %0A as a line
PHP email forms are the backbone of web communication, but they are also a primary target for attackers. The "V3.1 Exploit" refers to a specific class of vulnerabilities found in legacy or poorly patched validation scripts that allow for header injection and remote code execution (RCE). Instead of a standard email address, an attacker
Use str_replace() to strip \r and \n from any input used in email headers.
Most V3.1-style exploits rely on . This occurs when a script takes user input (like a name or subject) and places it directly into a PHP mail() function without proper sanitization.
If you must use the fifth parameter of mail() , wrap it in escapeshellarg() . Conclusion