CVSS9.1
Severitycritical
WeaknessCWE-1321
ExploitedNot in CISA KEV
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Description
Versions prior to 2.6.6 are vulnerable to prototype pollution via crafted missing-key strings when used to persist missing translation keys (e.g. via i18next-http-middleware's missingKeyHandler exposed to untrusted input). Backend.writeFile() splits each queued missing-key string on the configured keySeparator (default .) before calling the internal setPath() walker. The walker (getLastOfPath in lib/utils.js) did not guard against unsafe segments, so a key like "__proto__.polluted" was split into ["__proto__", "polluted"] and walked straight into Object.prototype, allowing an attacker to write arbitrary properties onto the global object prototype. Depending on the host application, polluted