CVE-2026-41690
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · unedited18next-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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidence18next-http-middleware versions prior to 3.9.3 allow unauthenticated HTTP clients to pollute Object.prototype via two unvalidated entry points (getResourcesHandler and missingKeyHandler). This prototype pollution can bypass authorization checks (e.g., user.isAdmin checks), cause type-confusion DoS, and potentially enable RCE depending on downstream code.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- High
- Availability
- Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed package versionRun 'npm list 18next-http-middleware' or check package.json dependencies to see the exact version number installedAffected if The version is lower than 3.9.3 (e.g., 3.9.2, 3.9.1, 3.8.x, etc.)
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Locate middleware usage in codeSearch codebase for imports of 18next-http-middleware and usages of 'getResourcesHandler' or 'missingKeyHandler' functions (e.g., grep for 'getResourcesHandler' or 'missingKeyHandler')Affected if These handlers are imported and used in the application code without additional input validation layers
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Verify handler exposure via HTTPCheck server configuration files (Express, Koa, Fastify, etc.) where the middleware is mounted - look for routes that expose i18n functionality (often under /locales, /translation, /resources, or the root path)Affected if The i18n handlers are mounted on publicly accessible HTTP routes without authentication middleware in front of them
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Inspect request parameter handlingReview how the middleware processes query parameters or body parameters - look for code that passes user input directly to the handlers without sanitization (e.g., checking for __proto__, constructor, or other prototype-affecting keys in incoming requests)Affected if The application does not filter or reject requests containing '__proto__', 'constructor', or similar prototype-polluting keys in request parameters
You are affected if 18next-http-middleware version is below 3.9.3 AND the getResourcesHandler or missingKeyHandler handlers are exposed via HTTP without input validation or authentication protecting them.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade to version 3.9.3 or later which implements proper input validation to prevent prototype pollution.
3.9.3
- Check the current version of 18next-http-middleware in your project by running: npm list 18next-http-middleware
- Upgrade to version 3.9.3 or later using: npm install 18next-http-middleware@^3.9.3
- Verify the upgrade was successful by running: npm list 18next-http-middleware
- Test your application to ensure the middleware functions correctly after the upgrade
- Rebuild and redeploy your application
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation1.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-41690 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-41690 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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