CVE-2026-41691: I18next http backend Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q89c-q3h5-w34g",
  "modified" : "2026-05-11T13:29:17Z",
  "published" : "2026-04-22T17:41:24Z",
  "aliases" : [ "CVE-2026-41691" ],
  "summary" : " i18next-http-backend has Path Traversal & URL Injection via Unsanitised lng/ns",
  "details" : "### Summary\n\nVersions of `i18next-http-backend` prior to 3.0.5 interpolate the `lng` and `ns` values directly into the configured `loadPath` / `addPath` URL template without any encoding, validation, or path sanitisation. When an application exposes the language-code selection to user-controlled input (the default — `i18next-browser-languagedetector` reads `?lng=` query params, cookies, `localStorage`, and request headers), an attacker can inject characters that change the structure of the outgoing request URL.\n\nAffected call sites:\n\n- `_readAny` — `lib/index.js:64`: `interpolate(resolvedLoadPath, { lng: languages.join('+'), ns: namespaces.join('+') })`\n- `create` — `lib/index.js:123` (pre-patch): `interpolate(addPath, { lng, ns: namespace })`\n\nThe helper `interpolate` (`lib/utils.js`) previously returned the raw value with no encoding. In contrast, `addQueryString` already correctly uses `encodeURIComponent` for each query-string param — only the URL-path substitution was unprotected.\n\n### Impact\n\nAn attacker who can influence the resolved `lng` or `ns` value can alter the URL in several ways:\n\n- **Path traversal** — `lng = '../../config'` turns `/locales/{{lng}}/{{ns}}.json` into `/locales/../../config/translation.json`. On a misconfigured web server, this can cause the request to target a different resource than intended; in SSR pipelines that use `file://` or similar schemes for `loadPath`, it can read arbitrary files from the host filesystem.\n- **Query-string injection** — `lng = 'en?admin=true'` turns `/locales/{{lng}}/{{ns}}.json` into `/locales/en?admin=true/translation.json`. Some server frameworks parse the query portion with higher priority than the path and branch on attacker-controlled flags.\n- **Fragment truncation** — `lng = 'en#anything'` silently discards the rest of the path in browser fetches (client cannot see the final URL).\n- **URL-encoded bypasses** — `lng = 'en%2F..'`, after server-side URL decoding, resolves to `en/..` — the attacker bypasses the absence of a literal `/` in their input.\n\nThe practical worst case is **SSRF** when `loadPath` is an internal or file-scheme URL, and **path-based authorisation bypass** against servers that segment access by URL prefix.\n\n### Also fixed in 3.0.5\n\n- **Per-instance `omitFetchOptions`.** A module-level boolean in `lib/request.js` was flipped to `true` the first time any backend instance hit a \"not implemented\" fetch error. Once flipped, **all** subsequent requests from **all** backend instances in the same module silently stripped every user-configured fetch option — including security-relevant `credentials`, `mode`, and `cache`. One misbehaving instance (for example during SSR hydration or in React Native) permanently removed these protections process-wide. 3.0.5 scopes the flag to the backend's `options` object (`options._omitFetchOptions`) so one instance's fallback cannot pollute siblings.\n- **Log forging via control characters in `lng`/`ns`.** Error callbacks embedded the raw `lng`/`ns`/URL in the message string. Crafted CR/LF values could inject fake log lines into file-backed log aggregators (CWE-117). 3.0.5 strips C0/C1 control chars before concatenation.\n- **Basic-auth credentials leaked into error callbacks.** If `loadPath` contained a `user:password@host` authority, the full URL (including the credentials) ended up in the error message strings returned to the caller. 3.0.5 redacts `user:password@` before logging.\n- **Prototype-pollution amplification via `for...in`.** `addQueryString` and the XHR `customHeaders` loop used `for...in` which walks the prototype chain. Polluted `Object.prototype` entries could leak into URL query parameters and request headers. 3.0.5 uses `Object.keys` and an explicit prototype-key guard.\n\n### Affected versions\n\nAll versions of `i18next-http-backend` prior to **3.0.5**.\n\n### Patch\n\nFixed in **3.0.5**. Summary of the hardening:\n\n1. New `utils.interpolateUrl` (used by `_readAny` and `create`) returns `null` if any substitution fails the URL-segment safety check (blocks `..`, `/`, `\\`, `?`, `#`, `%`, `@`, whitespace, control chars, prototype keys, and values > 128 chars). Multi-language joins (`en+de`) are validated per-segment. The call sites now refuse to issue a request when the check fails and call back with a clear error.\n2. `omitFetchOptions` is stored per-instance on `options._omitFetchOptions`.\n3. Error-callback messages sanitise strings and redact URL credentials.\n4. `for...in` over untrusted objects replaced with `Object.keys` + prototype-key guard.\n\n### Workarounds\n\nNo workaround short of upgrading. If you cannot upgrade immediately, sanitise `lng` / `ns` yourself before they reach i18next (strip `..`, `/`, `\\`, `?`, `#`, `%`, whitespace, and control characters; cap the length).\n\n### Credits\n\nDiscovered via an internal security audit of the i18next ecosystem.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "i18next-http-backend"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.0.5"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/i18next/i18next-http-backend/security/advisories/GHSA-q89c-q3h5-w34g"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-41691"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/i18next/i18next-http-backend/commit/4cee84f229c637b9c182366d3156f726d407a621"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/i18next/i18next-http-backend"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22", "CWE-74" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-22T17:41:24Z",
    "nvd_published_at" : "2026-05-07T21:16:29Z"
  }
}