Q: Which HTTP headers are considered malicious or harmful?

A: The following HTTP headers can be used for malicious purposes:

1. X-Forwarded-For: Used to spoof the client's real IP address, potentially bypassing IP-based restrictions.
2. Cookie: If not properly secured, cookies can be manipulated to impersonate users or gain unauthorised access.
3. User-Agent: Can be modified to hide the attacker's real operating system or browser, making fingerprinting harder.
4. Referer: Can be spoofed to launch phishing attacks or bypass CSRF protection that relies on referer checks.