GHSA-9G5Q-2W5X-HMXF

Vulnerability from github – Published: 2026-06-25 18:18 – Updated: 2026-06-25 18:18
VLAI
Summary
chi Middleware Vulnerable to Potential IP Spoofing via `X-Forwarded-For` Header in `Request.RemoteAddr` Resolution
Details

Summary

The vulnerability allows the Request.RemoteAddr to be spoofed when determining the request source IP via the X-Forwarded-For header. This could result in misidentification of the request source and potentially compromise access control and logging integrity.

Details

Currently, the RealIP() implementation splits the X-Forwarded-For header by , and uses the first IP. https://github.com/go-chi/chi/blob/v5.1.0/middleware/realip.go#L50-L54

However, relying on the first IP in the X-Forwarded-For header is insecure because it can be manipulated by attackers to falsify the source IP.

Malicious Case: 1. A malicious client sends a request with a forged IP in the X-Forwarded-For header: X-Forwarded-For: <forged-ip> 2. The proxy appends the actual client’s IP and forwards the request: X-Forwarded-For: <forged-ip>,<client-ip> 3. If the server always uses the first IP, it becomes vulnerable to IP spoofing.

Ideally, the implementation should verify IPs starting from the end of the X-Forwarded-For header value, skipping trusted IPs within the system, and using the first untrusted IP as the actual client IP.

For example, the labstack/echo web framework processes the X-Forwarded-For header by checking IPs from the end, skipping trusted IPs, and using the first untrusted IP as the client's ip. https://github.com/labstack/echo/blob/v4.13.2/ip.go#L261-L273

PoC

1. Run the Go application with the following code:

package main

import (
    "fmt"
    "log"
    "net/http"

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

func main() {
    // Set handler to print the remote address
    handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        fmt.Fprintln(
            w,
            fmt.Sprintf("remote addr: %s (want 192.0.2.1)", r.RemoteAddr),
        )
    })
    // Use RealIP middleware
    log.Fatal(http.ListenAndServe(":8080", middleware.RealIP(handler)))
}

2. Send a request to the server using curl with a manipulated X-Forwarded-For header:

$ curl localhost:8080 -H 'X-Forwarded-For: 192.0.2.2, 192.0.2.1'
remote addr: 192.0.2.2 (want 192.0.2.1)

Impact

This vulnerability can lead to a request source IP spoofing issue, which may allow attackers to bypass access controls or falsify request logs. It primarily affects systems that rely on X-Forwarded-For to determine the actual client IP, particularly in scenarios where intermediary proxies or load balancers are involved.

Severity
7.7 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/go-chi/chi/middleware"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.9.0"
            },
            {
              "last_affected": "1.5.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/go-chi/chi/v2/middleware"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "2.1.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/go-chi/chi/v3/middleware"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "3.3.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/go-chi/chi/v4/middleware"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "4.1.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/go-chi/chi/v5/middleware"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.3.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-346"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-25T18:18:56Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "### Summary\nThe vulnerability allows the `Request.RemoteAddr` to be spoofed when determining the request source IP via the `X-Forwarded-For` header. This could result in misidentification of the request source and potentially compromise access control and logging integrity.\n\n### Details\nCurrently, the `RealIP()` implementation splits the `X-Forwarded-For` header by `,` and uses the first IP.\nhttps://github.com/go-chi/chi/blob/v5.1.0/middleware/realip.go#L50-L54\n\nHowever, relying on the first IP in the `X-Forwarded-For` header is insecure because it can be manipulated by attackers to falsify the source IP.\n\nMalicious Case:\n1. A malicious client sends a request with a forged IP in the X-Forwarded-For header: `X-Forwarded-For: \u003cforged-ip\u003e`\n2. The proxy appends the actual client\u2019s IP and forwards the request: `X-Forwarded-For: \u003cforged-ip\u003e,\u003cclient-ip\u003e`\n3. If the server always uses the first IP, it becomes vulnerable to IP spoofing.\n\nIdeally, the implementation should verify IPs starting from the end of the `X-Forwarded-For` header value, skipping trusted IPs within the system, and using the first untrusted IP as the actual client IP.\n\nFor example, the `labstack/echo` web framework processes the `X-Forwarded-For` header by checking IPs from the end, skipping trusted IPs, and using the first untrusted IP as the client\u0027s ip.\nhttps://github.com/labstack/echo/blob/v4.13.2/ip.go#L261-L273\n\n### PoC\n#### 1. Run the Go application with the following code:\n```go\npackage main\n\nimport (\n    \"fmt\"\n    \"log\"\n    \"net/http\"\n\n    \"github.com/go-chi/chi/v5/middleware\"\n)\n\nfunc main() {\n    // Set handler to print the remote address\n    handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {\n        fmt.Fprintln(\n            w,\n            fmt.Sprintf(\"remote addr: %s (want 192.0.2.1)\", r.RemoteAddr),\n        )\n    })\n    // Use RealIP middleware\n    log.Fatal(http.ListenAndServe(\":8080\", middleware.RealIP(handler)))\n}\n```\n#### 2. Send a request to the server using curl with a manipulated X-Forwarded-For header:\n```\n$ curl localhost:8080 -H \u0027X-Forwarded-For: 192.0.2.2, 192.0.2.1\u0027\nremote addr: 192.0.2.2 (want 192.0.2.1)\n```\n\n### Impact\nThis vulnerability can lead to a request source IP spoofing issue, which may allow attackers to bypass access controls or falsify request logs. It primarily affects systems that rely on X-Forwarded-For to determine the actual client IP, particularly in scenarios where intermediary proxies or load balancers are involved.",
  "id": "GHSA-9g5q-2w5x-hmxf",
  "modified": "2026-06-25T18:18:56Z",
  "published": "2026-06-25T18:18:56Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/go-chi/chi/security/advisories/GHSA-9g5q-2w5x-hmxf"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/go-chi/chi"
    },
    {
      "type": "WEB",
      "url": "https://github.com/go-chi/chi/releases/tag/v5.3.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P",
      "type": "CVSS_V4"
    }
  ],
  "summary": "chi Middleware Vulnerable to Potential IP Spoofing via `X-Forwarded-For` Header in `Request.RemoteAddr` Resolution"
}



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