GHSA-jfgf-83c5-2c4m i18next-http-middleware has path traversal / SSRF via user-controlled language and namespace parameters

• npm i18next-http-middleware: < 3.9.3 → fixed in 3.9.3

Summary Versions of `i18next-http-middleware` prior to 3.9.3 pass the user-controlled `lng` and `ns` values from `getResourcesHandler` directly into `i18next.services.backendConnector.load(languages, namespaces, …)` without any sanitisation. Depending on which backend is configured, the unvalidated path segments enable one of two attacks: • Filesystem path traversal when the middleware is paired with `i18next-fs-backend` (or any backend that interpolates `lng` / `ns` into a filesystem path). • Server-Side Request Forgery (SSRF) when the middleware is paired with `i18next-http-backend` (or any backend that interpolates into an HTTP URL). Example request: ``` GET /locales/resources.json?lng=../../etc/passwd&ns=root ``` with `i18next-fs-backend` reads the attacker-chosen file from disk; with `i18next-http-backend` reshapes the outgoing URL to target an internal service. Impact • Arbitrary file read via `fs`-style backends — any file the Node process can read becomes reachable (source, configuration, `.ssh` keys, `.env`, Docker secrets, etc.). • SSRF via `http`-style backends — requests to internal IPs / hostnames not normally reachable from the internet; combined with cloud metadata endpoints this can escalate to credential theft. • Unbounded growth of `i18next.options.ns` — a now-incidental amplification: the pre-patch `getResourcesHandler` pushed every unique `ns` value into the shared `i18next.options.ns` singleton array without validation or bounds, enabling memory exhaustion from repeated unique payloads. The severity is bounded by the backend in place, but the middleware itself exposed the unsanitised path; this is the "weakest link" layer. Affected versions `< 3.9.3`. Patch Fixed in 3.9.3. The patch introduces `utils.isSafeIdentifier` and applies it in `getResourcesHandler` before `lng` and `ns` reach the backend connector: ```js languages = languages.filter(utils.isSafeIdentifier) namespaces = namespaces.filter(utils.isSafeIdentifier) ``` `isSafeIdentifier` uses a denylist approach — it still accepts any legitimate i18next language-code shape (i18next FAQ) — rejecting: • `..` sequences (relative path traversal) • path separators (`/`, `\`) • control characters (C0/C1) • prototype keys (`__proto__` / `constructor` / `prototype`) • empty strings and values longer than 128 characters Unsafe values are dropped; only safe values reach the backend. The fix is a defence-in-depth layer on top of any sanitisation the backend itself may apply. Workarounds No workaround short of upgrading. Front-proxying the middleware with a WAF rule that rejects requests containing `..`, `/`, `\`, or URL-structure characters in `lng` / `ns` is a partial mitigation. Upgrading the configured backend (`i18next-fs-backend` ≥ 2.6.4, `i18next-http-backend` ≥ 3.0.5) also closes the same attack at the next layer. Related advisories fixed in the same release • GHSA-5fgg-jcpf-8jjw — prototype pollution via `setPath` and `missingKeyHandler`. Independently fixable, filed separately per CNA rules. • GHSA-c3h8-g69v-pjrg — HTTP response splitting + XSS-filter bypass (CVE-2026-41683). Credits Discovered via an internal security audit of the i18next ecosystem. Resources • CWE-22: Path Traversal • CWE-918: Server-Side Request Forgery (SSRF) (specific sub-case when paired with an HTTP backend) • i18next FAQ: language code formatting