CVE-2026-41690: i18next i18next-HTTP-Middleware

High severity, CVSS 8.6. EPSS: 0.5% chance of exploitation in the next 30 days.

18next-http-middleware is a middleware to be used with Node.js web frameworks like express or Fastify and also for Deno. Versions prior to 3.9.3 allow an unauthenticated HTTP client to pollute Object.prototype in the Node.js process hosting the middleware, via two unvalidated entry points that reach internal object-key writes: getResourcesHandler and missingKeyHandler. This can break authorisation checks (if (user.isAdmin) returning true for any user), cause type-confusion DoS, and depending on downstream code it can be chained into RCE.

Affected products

• i18next i18next-HTTP-Middleware: before 3.9.3 (fixed in 3.9.3)

Published 2026-05-08. Last modified 2026-06-17.