Can $_SERVER['REMOTE_ADDR'] Be Faked for Remote Requests?

Faking $_SERVER['REMOTE_ADDR'] for Remote Requests

Question:

Is it possible to forge or modify the $_SERVER['REMOTE_ADDR'] variable in order to misrepresent the origin IP address of a request?

Answer:

Yes, it is possible to fake the $_SERVER['REMOTE_ADDR'] variable for requests originating from a remote source. However, the feasibility of doing so depends on the intended method of manipulation.

Forged TCP Headers

Directly forging TCP headers to alter the source IP address is a potential method, but this approach requires advanced networking skills and is typically not straightforward to accomplish with PHP.

Compromising Network Gateways

If a network gateway such as a Wi-Fi router or ISP's outbound router is compromised, an attacker can effectively impersonate any device connected to that gateway. This would allow them to fake the $_SERVER['REMOTE_ADDR'] variable.

Additional Considerations

• Frameworks may implement checks for the X-HTTP-FORWARDED-FOR header, which can potentially be manipulated to alter the perceived source IP address.
• Loopback addresses cannot be reliably faked under TCP unless the local machine or server has been compromised.

Importance of Security

It is crucial to be aware of these techniques and take appropriate security measures, such as disabling checks for the X-HTTP-FORWARDED-FOR header in frameworks where necessary.

Relevant Blog Post

For further insights, refer to the following blog post:

[How I Hacked StackOverflow](link)

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