Which of the following involves sending arbitrary characters in a web page request?

SMS (Short Message Service) is a text messaging service for mobile phones and is unrelated to web page requests or injection attacks.

SSL (Secure Sockets Layer) is a protocol for establishing authenticated and encrypted links between networked computers, used for secure communication, not for sending arbitrary characters in an attack.

Cross-Site Scripting (XSS) attacks involve injecting malicious scripts, often containing arbitrary characters or code, into otherwise benign and trusted websites. When a user visits the compromised page, these scripts are executed in their browser, potentially stealing cookies, session tokens, or other sensitive information.

A VPN (Virtual Private Network) provides a secure, encrypted tunnel over a public network, but it does not inherently involve sending arbitrary characters in web requests as an attack vector.