Chi Framework ClientIPFromXFF Trusted CIDR Bypass

Executive Summary

This is a client IP spoofing vulnerability in the Golang Chi web framework's ClientIPFromXFF middleware. It fails to verify that the direct TCP peer in http.Request.RemoteAddr belongs to a trusted CIDR range before trusting X-Forwarded-For headers. An attacker who can directly reach the Go server can append a trusted-looking proxy address and manipulate the client IP returned by middleware.GetClientIP.

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Detection Guidance

To detect this vulnerability, inspect your Go applications using the Chi framework for versions prior to 5.4.0. Check if the ClientIPFromXFF middleware is enabled and review HTTP request logs for suspicious X-Forwarded-For headers containing trusted proxy IPs. Use commands like 'go list -m all' to check Chi versions and 'grep -r ClientIPFromXFF' to find middleware usage.

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Impact Analysis

An attacker could bypass IP-based access controls by spoofing a trusted client IP. This may lead to unauthorized access to protected endpoints, allowing the attacker to impersonate legitimate users or systems. The attack requires no authentication or user interaction.

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Compliance Impact

This vulnerability could potentially impact compliance with GDPR and HIPAA by allowing IP spoofing, which may undermine IP-based access controls or logging mechanisms that rely on accurate client IP identification. Unauthorized access to protected endpoints could lead to data breaches or improper access to sensitive information.

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Mitigation Strategies

Immediately upgrade the Chi framework to version 5.4.0 or later. If upgrading is not possible, disable the ClientIPFromXFF middleware or implement custom IP validation to verify RemoteAddr against trusted CIDR ranges before trusting X-Forwarded-For headers.

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