GHSA-5fgg-jcpf-8jjw

### Summary Versions of `i18next-http-middleware` prior to 3.9.3 pass user-controlled `lng` and `ns` parameters to two internal paths that use them in ways that enable prototype pollution and, depending on the configured backend, path traversal or SSRF. The vulnerable entry points are unauthenticated HTTP handlers that are part of the middleware's public API: - `getResourcesHandler` — reads `lng`/`ns` from query parameters or route params and passes them unvalidated to: - `utils.setPath(resources, [lng, ns], ...)` — the `setPath` helper did not guard against `__proto__`, `constructor`, or `prototype` keys, writing into `Object.prototype` when those values were supplied. - `i18next.services.backendConnector.load(languages, namespaces, ...)` — depending on the configured backend, unvalidated path segments enabled filesystem path traversal (e.g. with `i18next-fs-backend`) or SSRF (e.g. with `i18next-http-backend`). - A `namespaces.forEach(ns => i18next.options.ns.push(ns))` loop additionally performed permanent, unbounded growth of the shared singleton namespace list. - `missingKeyHandler` — iterated the incoming request body with `for...in`, which traverses inherited prototype-chain properties. A POST body like `{"__proto__": {"isAdmin": true}}` was forwarded into `saveMissing`. ### Impact - **Prototype pollution** — a single unauthenticated request of the form `GET /locales/resources.json?lng=__proto__&ns=isAdmin` writes into `Object.prototype`, affecting every plain object created subsequently in the Node.js process. This can break authorization checks (`if (user.isAdmin)`), cause denial of service via type confusion, or be chained into RCE depending on what downstream code reads from polluted objects. - **Path traversal / SSRF** — with filesystem or HTTP backends that interpolate `lng`/`ns` into paths or URLs, attacker-controlled values like `ns=../../etc/passwd` or `lng=internal-service` could reach resources outside the intended scope. - **Denial of se