{"cve":"CVE-2026-48714","nvd":{"published":"2026-06-15T22:16:17.550","modified":"2026-10-25T23:10:00.167","status":"Analyzed","description":"i18next-http-middleware is a middleware to be used with Node.js web frameworks like express or Fastify and also for Deno. In versions prior to 3.9.7, the missingKeyHandler blocked the literal request-body keys __proto__, constructor, and prototype (added in 3.9.3, see GHSA-5fgg-jcpf-8jjw), but did not reject dotted variants such as \"__proto__.polluted\". Downstream backends that split the missing-key string on a configured keySeparator (notably i18next-fs-backend ≤ 2.6.5) hand these keys to an unguarded setPath() walker that writes to Object.prototype. Applications that expose missingKeyHandler to untrusted input AND use i18next-fs-backend ≤ 2.6.5 are directly exploitable for remote prototype pollution. Other downstream backends that split the missing-key string the same way may be similarly affected. Depending on the host application, polluted prototype properties may cause crashes, corrupted translation behaviour, configuration poisoning, or bypasses of property-based security checks. This issue has been fixed in version 3.9.7.  If developers cannot upgrade immediately, they should do the following: do not expose missingKeyHandler to untrusted users (mount it behind authentication, or remove the route), add a request-body filter ahead of the handler that rejects any top-level key containing __proto__, constructor, or prototype after splitting on their configured keySeparator, and disable missing-key persistence (saveMissing: false) when accepting writes from untrusted input.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H","score":9.1},"cwes":["CWE-1321"],"references":["https://github.com/i18next/i18next-http-middleware/commit/7c6d26f137d3e940b8d229ca148bca38845faf49","https://github.com/i18next/i18next-http-middleware/security/advisories/GHSA-f49m-vf83-692w"],"products":["i18next:i18next-http-middleware"],"source":"nvd","synced_at":"2026-10-25T23:44:33.281319194+00:00"},"epss":{"cve":"CVE-2026-48714","score":0.00507,"percentile":0.42968,"date":"2026-10-25"},"kev":null,"osv":[{"id":"GHSA-f49m-vf83-692w","url":"https://osv.dev/vulnerability/GHSA-f49m-vf83-692w","summary":"i18next-http-middleware: MissingKeyHandler does not reject keys whose segments contain prototype-polluting names","modified":"2026-06-25T17:56:29.524803Z","packages":[{"ecosystem":"npm","name":"i18next-http-middleware","purl":"pkg:npm/i18next-http-middleware","ranges":["<3.9.7"],"fixed":["3.9.7"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}