i18next-fs-backend vulnerable to prototype pollution via crafted missing-key string

Weakness-Klassen (CWE)

• CWE-1321Variant

  Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

  The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.

  cwe.mitre.org →

Re-Analyse & Statuswechsel

Chronologie der NVD-Audit-Events für diese CVE — Reanalyses, CVSS-Updates, CPE-Diffs.

1. Initial Analysis2026-06-17 16:39 UTC· nvd@nist.gov
   • CPE Configuration: OR *cpe:2.3:a:i18next:i18next-fs-backend:*:*:*:*:*:node.js:*:* versions up to (excluding) 2.6.6
   • Reference Type: GitHub, Inc.: https://github.com/i18next/i18next-fs-backend/commit/3ab0448087da6935a40117f904b7457281f963f4 Types: Patch
   • Reference Type: GitHub, Inc.: https://github.com/i18next/i18next-fs-backend/security/advisories/GHSA-2933-q333-qg83 Types: Mitigation, Vendor Advisory
2. New CVE Received2026-06-15 22:16 UTC· security-advisories@github.com
   • 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 prototype properties may cause crashes, corrupted translation behaviour, configuration poisoning, or bypasses of property-based security checks. Applications are affected only if the missingKeyHandler (or another route that forwards untrusted request bodies to i18next.t(..., { ... }) with saveMissing: true) is reachable by untrusted users and the default behaviour of splitting missing-key strings on keySeparator is in use (i.e. keySeparator is not false). Apps that do not expose missing-key persistence to untrusted input are not directly affected through this attack path. This issue has been fixed in version 2.6.6. If developers using the library are unable to upgrade immediately, they should take the following precautions: do not expose i18next-http-middleware's missingKeyHandler to untrusted users (mount it behind authentication, or remove the route), disable missing-key persistence (saveMissing: false, or no backend.create implementation) when accepting writes from untrusted input, and set keySeparator: false in their i18next options to disable backend key splitting (note: this also disables nested translation keys).
   • CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
   • CWE: CWE-1321
   • Reference: https://github.com/i18next/i18next-fs-backend/commit/3ab0448087da6935a40117f904b7457281f963f4

Betroffene Produkte

Aus der Hersteller-/CERT-Meldung extrahierte Produkte und Versionsbereiche. Ein Version-Range wie „<4.14.6“ impliziert die Update-Empfehlung „auf 4.14.6 oder höher aktualisieren“.

• npm

  i18next-fs-backend

Quellen & Referenzen

• https://github.com/i18next/i18next-fs-backend/security/advisories/GHSA-2933-q333-qg83
  web
• https://nvd.nist.gov/vuln/detail/CVE-2026-48713
  advisory
• https://github.com/i18next/i18next-fs-backend/commit/3ab0448087da6935a40117f904b7457281f963f4
  web
• https://github.com/i18next/i18next-fs-backend
  package

Verknüpfte Empfehlungen

• sans-atrisk-mail2026-06-18 00:00 UTC
  @RISK®: The Consensus Security Vulnerability Alert: Vol. 26, Num. 24