{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "i18next-locize-backend"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "9.0.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-22",
      "CWE-74"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-22T20:28:27Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nVersions of `i18next-locize-backend` prior to 9.0.2 interpolate `lng`, `ns`, `projectId`, and `version` directly into the configured `loadPath` / `privatePath` / `addPath` / `updatePath` / `getLanguagesPath` URL templates with no path-component validation and no encoding. When an application exposes any of these values to user-controlled input (`?lng=` / `?ns=` query parameters via `i18next-browser-languagedetector`, cookies, request headers, or a URL-derived `projectId`), a crafted value can change the structure of the outgoing request URL.\n\nAffected call sites in `lib/index.js` (pre-patch): the `interpolate()` helper is used at the five URL-build sites \u2014 `_readAny`/`read` (line 415 for private, 426 for public), `getLanguages` (lines 271 and 296), and `writePage` (lines 616 and 622) for the missing-key and update POST paths. The helper `interpolate` in `lib/utils.js` substitutes raw values with no encoding.\n\n### Impact\n\nAn attacker who can influence `lng`, `ns`, `projectId`, or `version` can:\n\n- **Path traversal** \u2014 `lng = \u0027../../admin\u0027` against `https://api.locize.app/{{projectId}}/{{version}}/{{lng}}/{{ns}}` changes the request URL path segment that reaches the locize CDN / API.\n- **Query-string injection** \u2014 `lng = \u0027en?x=y\u0027` appends an attacker-chosen query to the URL.\n- **Fragment truncation** \u2014 `lng = \u0027en#x\u0027` silently truncates the path in browser fetches.\n- **URL-encoded bypass** \u2014 `lng = \u0027en%2F..\u0027` leverages server-side decoding to reintroduce `/..`.\n\nThe worst-case concrete impact is loading an unintended translation resource (potentially causing wrong content to render) and, when a custom `loadPath` is configured against an internal / file-scheme URL, **SSRF or arbitrary-file read** on the host running the backend.\n\nAdditionally, the pre-patch `interpolate()` function read `data[key]` without excluding prototype-chain properties \u2014 under prototype-pollution conditions in the same process, that path could pull values from `Object.prototype` into the URL.\n\n### Related fixes shipped in 9.0.2\n\n- The `defaults()` helper replaces `for...in` iteration with `Object.keys()` plus an explicit prototype-key guard so a polluted `Object.prototype` cannot leak into the merged options object.\n- New `utils.interpolateUrl` / `isSafeUrlSegment` / `sanitizeLogValue` / `redactUrlCredentials` helpers mirror the pattern shipped in `i18next-http-backend@3.0.5` (see its advisory [GHSA-q89c-q3h5-w34g](https://github.com/i18next/i18next-http-backend/security/advisories/GHSA-q89c-q3h5-w34g)).\n\n### Affected versions\n\nAll versions of `i18next-locize-backend` prior to **9.0.2**.\n\n### Patch\n\nFixed in **9.0.2**. `lib/index.js` now uses `interpolateUrl()` at every URL-build site and returns an error callback (or silently drops the queued write for `writePage`) when any interpolated value fails the safety check. Legitimate i18next language-code shapes (BCP-47, `en_US`, `zh-Hant-HK`, `my-custom.ns`, `+`-joined multi-language values) all pass.\n\n### Workarounds\n\nNo workaround short of upgrading. If you cannot upgrade immediately, sanitise `lng` / `ns` / `projectId` / `version` at your application boundary before passing them through to i18next \u2014 reject values containing `..`, `/`, `\\`, `?`, `#`, `%`, whitespace, control characters, and cap the length.\n\n### Credits\n\nDiscovered via an internal security audit of the i18next / locize ecosystem.\n\n### References\n\n- [CWE-22: Path Traversal](https://cwe.mitre.org/data/definitions/22.html)\n- [CWE-74: Injection](https://cwe.mitre.org/data/definitions/74.html)\n- [CWE-1321: Prototype Pollution (amplification path)](https://cwe.mitre.org/data/definitions/1321.html)\n- Related advisory in the same ecosystem: [GHSA-q89c-q3h5-w34g (i18next-http-backend)](https://github.com/i18next/i18next-http-backend/security/advisories/GHSA-q89c-q3h5-w34g)",
  "id": "GHSA-mgcp-mfp8-3q45",
  "modified": "2026-04-22T20:28:27Z",
  "published": "2026-04-22T20:28:27Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/locize/i18next-locize-backend/security/advisories/GHSA-mgcp-mfp8-3q45"
    },
    {
      "type": "WEB",
      "url": "https://github.com/locize/i18next-locize-backend/commit/8f81ad4707aa0e90647fde4da5fbe5b23153c6e1"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/locize/i18next-locize-backend"
    },
    {
      "type": "WEB",
      "url": "https://github.com/locize/i18next-locize-backend/releases/tag/v9.0.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "i18next-locize-backend has URL Injection via Unsanitized Path Parameters"
}