CVE-2026-72815 in chi
Summary
by MITRE • 08/14/2026
go-chi chi versions >= 5.2.1 and before 5.3.0 contain an IP spoofing vulnerability in the RealIP middleware, which blindly trusts the first (leftmost) value of the X-Forwarded-For HTTP header. A remote attacker can bypass IP-based access control lists and rate-limiting mechanisms, and forge log entries, by supplying a spoofed IP address in the X-Forwarded-For header. The issue is fixed in version 5.3.0.
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Analysis
by VulDB Data Team • 08/14/2026
The vulnerability exists within the go-chi web framework's RealIP middleware component affecting versions between 5.2.1 and 5.2.9 inclusive. This represents a critical security flaw that undermines fundamental network security controls by enabling attackers to manipulate IP address identification mechanisms. The issue stems from the middleware's blind trust in the X-Forwarded-For HTTP header, which is commonly used in web applications to determine the original client IP address when requests pass through proxies or load balancers. When the RealIP middleware processes this header, it only considers the first value present in the comma-separated list, completely disregarding the possibility that this value may have been maliciously crafted by an attacker.
The technical implementation of this vulnerability allows for significant operational compromise within web applications that rely on IP-based access control mechanisms. Attackers can exploit this flaw by crafting HTTP requests with spoofed X-Forwarded-For headers containing arbitrary IP addresses, effectively bypassing any network-level restrictions or rate-limiting controls that depend on source IP validation. This manipulation enables unauthorized access to protected resources, circumvention of security policies, and potential abuse of application functionality through techniques such as brute force attacks or denial-of-service amplification. The vulnerability specifically maps to CWE-284 Access Control Bypass and aligns with ATT&CK technique T1071.004 Application Layer Protocol: DNS, as it enables attackers to manipulate network traffic routing through falsified client identification.
The operational impact of this vulnerability extends beyond simple access control bypasses, as it fundamentally compromises the integrity of application logs and audit trails. When log entries contain forged IP addresses due to this vulnerability, security operations teams face significant challenges in conducting forensic analysis or threat hunting activities. The forged IP addresses can mask actual attack sources, leading to incorrect attribution of malicious activities and potentially allowing attackers to remain undetected within network environments. Additionally, the vulnerability undermines the effectiveness of any security controls that depend on accurate client identification for policy enforcement, including geographic restrictions, user access controls, and automated threat detection systems.
Organizations utilizing affected go-chi versions should immediately implement mitigations while planning for the mandatory upgrade to version 5.3.0 or later. The most effective immediate solution involves implementing additional validation layers within application code that verify the authenticity of IP addresses before relying on the X-Forwarded-For header values. This can include configuring reverse proxies to properly sanitize headers, implementing strict header validation rules, and establishing multi-factor authentication mechanisms that do not solely rely on IP-based controls. Security teams should also conduct comprehensive network scans to identify all affected systems and review existing access control policies to ensure they account for potential IP spoofing attacks. The fix in version 5.3.0 addresses the core issue by implementing proper header parsing and validation logic that considers the trustworthiness of forwarded IP addresses rather than blindly accepting the first value in the X-Forwarded-For header chain.