{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/go-chi/chi"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "5.2.2"
            },
            {
              "fixed": "5.2.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-601"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-01-14T21:18:06Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nThe `RedirectSlashes` function in middleware/strip.go does not perform correct input validation and can lead to an open redirect vulnerability.\n\n### Details\n\nThe `RedirectSlashes` function performs a `Trim` to all forward slash (`/`) characters, while prepending a single one at the begining of the path (Line 52).\n\nHowever, it does not trim backslashes (`\\`).\n\n```go\nFile: middleware/strip.go\n41: func RedirectSlashes(next http.Handler) http.Handler {\n...\n51: \t\t\t// Trim all leading and trailing slashes (e.g., \"//evil.com\", \"/some/path//\")\n52: \t\t\tpath = \"/\" + strings.Trim(path, \"/\")\n...\n62: }\n```\n\nAlso, from version 5.2.2 onwards the `RedirectSlashes` function does not take into consideration the `Host` Header in the redirect response returned. This was done in order to combat another [[vulnerability](https://github.com/go-chi/chi/security/advisories/GHSA-vrw8-fxc6-2r93)](https://github.com/go-chi/chi/security/advisories/GHSA-vrw8-fxc6-2r93).\n\nThe above make it possible for a response in the following form:\n\n```\nHTTP/1.1 301 Moved Permanently\nLocation: /\\evil.com\n```\n\nThe `/\\evil.com` will be transformed by most browsers (Chrome, Firefox, etc. not Safari) into `//evil.com` which is a protocol relative URL and will result in a redirect to `evil.com`, essentially making it an open redirect vulnerability.\n\n### PoC\n\nA minimal working example can be seen below.\n\n```go\npackage main\n\nimport (\n\t\"fmt\"\n\t\"net/http\"\n\n\t\"github.com/go-chi/chi/v5\"\n\t\"github.com/go-chi/chi/v5/middleware\"\n)\n\n\n\nfunc main() {\n\tr := chi.NewRouter()\n\n\tr.Use(middleware.RedirectSlashes)\n\n\tr.Get(\"/*\", func(w http.ResponseWriter, r *http.Request) {\n\t\tw.WriteHeader(http.StatusOK)\n\t})\n\n\tfmt.Println(\"Server starting on port 8081...\")\n\tif err := http.ListenAndServe(\":8081\", r); err != nil {\n\t\tfmt.Printf(\"Error starting server: %v\\n\", err)\n\t}\n}\n\n```\n\nAnd when we request the path `/\\evil.com` (needs a second backslash or URL encoding in the terminal), the HTTP Redirect Location is just `/\\evil.com` without any domain/Host information.\n\n```bash\n$ curl -I  localhost:8081/\\\\evil.com/\nHTTP/1.1 301 Moved Permanently\nContent-Type: text/html; charset=utf-8\nLocation: /\\evil.com\n```\n\n```bash\n$ curl -I  localhost:8081/%5Cevil.com/\nHTTP/1.1 301 Moved Permanently\nContent-Type: text/html; charset=utf-8\nLocation: /\\evil.com\n```\n\nThis opened in a browser (Chrome, Firefox) will result in a transformation to `//evil.com` which in turn will result in a redirect to `evil.com`.\n\u003cimg width=\"200\" alt=\"image-20250829115619807\" src=\"https://github.com/user-attachments/assets/44aedad1-64b6-4660-8b26-fad9b4eca036\" /\u003e\n\n\n\u003cimg width=\"200\" alt=\"image-20250829115632067\" src=\"https://github.com/user-attachments/assets/b976d47d-1975-469c-abd3-deb907a68db2\" /\u003e\n\n\n### Impact\n\nThis essentially consists of an open redirect vulnerability, provided that victim users use the most popular browsers (Chrome, Firefox, etc. It does not work in e.g. Safari).\n\nThe attacker can construct a malicious URL on a domain of a legitimate website and send it to the victim user. The victim users thinking that they will click on a legitimate website\u0027s URL, they will unknowingly be reidrected to an attacker controlled website.\n\nThis can lead to credential theft if the victim gets redirected to a phishing website, to malware that is hosted on the attacker controlled website etc. Also, it has a greate reputation / business impact for the affected legitimate website.\n\nIn order to exploit this vulnerability the attacker does not need to be authenticated or have ay other priviledge / knowledge regarding the affected application.\n\nCVSS Score: [4.7 (Medium)](https://www.first.org/cvss/calculator/3-0#CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N)",
  "id": "GHSA-mqqf-5wvp-8fh8",
  "modified": "2026-01-14T21:18:06Z",
  "published": "2026-01-14T21:18:06Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/go-chi/chi/security/advisories/GHSA-mqqf-5wvp-8fh8"
    },
    {
      "type": "WEB",
      "url": "https://github.com/go-chi/chi/issues/1037"
    },
    {
      "type": "WEB",
      "url": "https://github.com/go-chi/chi/commit/6eb35881c0e438ffb663ddbad3a61babaa5e5d8a"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/go-chi/chi"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "chi has an open redirect vulnerability in the RedirectSlashes middleware"
}