Here's an example of an exploit:
mail($to, $subject, 'Hello World!', $headers); In this example, the attacker injects a malicious X-Forwarded-For header, which includes a command to execute ( cat /etc/passwd ). The mail() function will then execute this command, allowing the attacker to access sensitive system files.
The vulnerability exists due to the lack of proper input validation in the mail() function, allowing an attacker to inject arbitrary data, including command-line arguments. This can lead to a remote code execution (RCE) vulnerability, enabling an attacker to execute arbitrary system commands.
The vulnerability you're referring to is likely related to a remote code execution (RCE) vulnerability in PHP, specifically in the mail() function, which is commonly used in contact forms.