{"id":"CVE-2026-41885","aliases":["GHSA-mgcp-mfp8-3q45"],"url":"https://o3.security/vulnerability/CVE-2026-41885","summary":"Path traversal / URL injection via unsanitised lng/ns/projectId/version in i18next-locize-backend","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 — `_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** — `lng = '../../admin'` 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** — `lng = 'en?x=y'` appends an attacker-chosen query to the URL.\n- **Fragment truncation** — `lng = 'en#x'` silently truncates the path in browser fetches.\n- **URL-encoded bypass** — `lng = 'en%2F..'` 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 — 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 — 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)","published":"2026-05-08T15:41:14.065Z","modified":"2026-08-12T03:51:18.414589628Z","cvss":{"score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N"},"epss":{"score":0.00224,"percentile":0.13116,"asOf":"2026-08-14"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"i18next-locize-backend","fixedVersion":"9.0.2"}],"fix":{"url":"https://github.com/locize/i18next-locize-backend/commit/8f81ad4707aa0e90647fde4da5fbe5b23153c6e1","label":"locize/i18next-locize-backend@8f81ad4"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/41xxx/CVE-2026-41885.json"},{"type":"ADVISORY","url":"https://github.com/locize/i18next-locize-backend/security/advisories/GHSA-mgcp-mfp8-3q45"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-41885"},{"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:18.414589628Z"}}