[BUG] using local proxy allows circumventing restricted IP addresses

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

https://www.youtube.com/watch?v=LtvOUpfZz4M - in this video a Russian user is using Claude Code and Claude Desktop via his local proxy running at the same computer.

What Should Happen?

To improve IP detection, Claude could check the "X-Forwarded-For" HTTP-header

Error Messages/Logs

Steps to Reproduce

n/a

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

n/a

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_