IP Spoofing in go-chi/chi RealIP Middleware

Executive Summary

This vulnerability is an IP spoofing issue in the go-chi/chi web framework versions 0.9.0 to 5.2.0. The RealIP middleware incorrectly uses the first IP in the X-Forwarded-For header as the request source IP without validating trusted proxies. Attackers can forge this header to falsify their IP address, potentially bypassing access controls or manipulating request logs.

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Detection Guidance

To detect this vulnerability, inspect HTTP request headers for manipulated X-Forwarded-For values. Check if your application uses go-chi/chi versions before 5.3.0. Monitor logs for inconsistencies between RemoteAddr and X-Forwarded-For headers. Test by sending requests with forged X-Forwarded-For headers to see if the server accepts them.

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Impact Analysis

This vulnerability could allow attackers to bypass access controls by spoofing their IP address, leading to unauthorized access to restricted resources. It may also falsify request logs, making it difficult to trace malicious activities. Systems using proxies or load balancers are particularly vulnerable.

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Mitigation Strategies

Upgrade go-chi/chi to version 5.3.0 or later. Configure the RealIP middleware to validate trusted proxies and use the last untrusted IP in the X-Forwarded-For header. Implement network-level controls to block requests with suspicious headers. Review and update access control policies to account for potential IP spoofing.

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