js2i18next() is vulnerable to prototype pollution. When converting translations, it splits nested keys on the key separator (default ##) and uses each segment as a dynamic object key while building the output object. A key whose segment is proto (e.g. proto ##gcPolluted) causes the converter to resolve Object.prototype as the nested write target and assign the translated value onto it, polluting Object.prototype for the whole runtime.

Any application that converts translation data (PO / i18next JS objects) originating from an untrusted or user-controlled source is affected. Prototype pollution can lead to denial of service and, depending on the surrounding application, may enable further attacks.

Fixed in gettext-converter@1.3.3. Key segments equal to proto, constructor, or prototype are now rejected before being used as dynamic object keys.

Upgrade to 1.3.3. If upgrading is not immediately possible, sanitize/validate translation keys before passing them to js2i18next() and reject any key whose ##-separated segments include proto, constructor, or prototype.