CVE-2026-118258: i18next-http-backend: Query-parameter injection through & and = in lng when loadPath/addPath puts {{lng}} in the query string

The URL-segment check added for GHSA-q89c-q3h5-w34g blocks ?, #, %, :, / and @ in lng, but not & or =, and the checked value is inserted into the URL without encoding. The README documents a multiload loadPath of the form /locales/resources.json?lng=de+en&ns=ns1+ns2. With a template like that, an attacker who controls the language value can add or override query parameters on the request the backend sends. By default the language comes from ?lng=, a cookie or Accept-Language. This is the “query-string injection” impact described in GHSA-q89c; only the ? form was closed.

Server side (Express + i18next-http-middleware, default options), GET /?lng=de%26ns%3Dprivate%26admin%3Dtrue makes the application request …?lng=de&ns=private&admin=true&ns=common from its own translations API.