CVE-2026-41683
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 · uneditedi18next-http-middleware is a middleware to be used with Node.js web frameworks like express or Fastify and also for Deno. Prior to version 3.9.3, i18next-http-middleware wrote user-controlled language values into the Content-Language response header after passing them through utils.escape(), which is an HTML-entity encoder that does not strip carriage return, line feed, or other control characters. When the application used an older i18next (< 19.5.0) that still exercised the backward-compatibility fallback at LanguageDetector.js:100 or otherwise produced a raw detected value, CRLF sequences in the attacker-controlled lng parameter reached res.setHeader('Content-Language', ...) verbatim. This issue has been patched in version 3.9.3.
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 confidencei18next-http-middleware before 3.9.3 is vulnerable to HTTP Response Splitting/Header Injection. User-supplied language parameters containing CRLF sequences are written to the Content-Language response header via utils.escape(), which encodes HTML entities but does not strip carriage return or line feed characters. When used with i18next versions prior to 19.5.0, raw detected language values pass through without sanitization, allowing attackers to inject arbitrary headers or split HTTP responses.
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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Check i18next-http-middleware versionRun 'npm list i18next-http-middleware' or check package.json dependencies to identify the installed versionAffected if Version is lower than 3.9.3
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Check i18next versionRun 'npm list i18next' or check package.json dependencies to identify the installed versionAffected if Version is lower than 19.5.0 (the version that eliminates the backward-compatibility fallback path)
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Verify Content-Language header usageSearch codebase for usages of 'Content-Language' header or i18next-http-middleware's language detection that writes to response headersAffected if The application uses language detection that writes to Content-Language header and passes user-supplied language values
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Check for language parameter handlingInspect code that handles language detection from incoming requests (query params, headers, cookies) and trace whether these values flow through to response headers without sanitizationAffected if User-supplied language values from requests are used without stripping CRLF characters before being set as response headers
You are affected if i18next-http-middleware is below version 3.9.3 AND your application uses language detection that writes to Content-Language headers with user-supplied input, especially if i18next is also below 19.5.0.
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 i18next-http-middleware to version 3.9.3 or later. Additionally, upgrading to i18next >= 19.5.0 is recommended to eliminate the backward-compatibility fallback path that exposes raw detected values.
3.9.3
- Check the current version of i18next-http-middleware in your project dependencies (package.json)
- Update i18next-http-middleware to version 3.9.3 or later using your package manager (e.g., npm install [email protected] or yarn upgrade [email protected])
- Verify the upgrade was successful by running npm list i18next-http-middleware or checking installed version
- Test your application's language detection functionality to ensure the Content-Language header is set correctly
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing3.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-41683 — 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-2026-41683 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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