i18next-http-middleware: HTTP response splitting and DoS via unsanitised Content-Language header

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.6 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

EPSS

• CVE-2026-41683: 0.33% estimated exploitation activity in the next 30 days; percentile 25.90 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Versions of i18next-http-middleware prior to 3.9.3 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. Impact Two concrete outcomes depending on the Node.js version: - Node.js < 14.6.0 — HTTP response splitting. An attacker crafting a request like GET /?lng=en%0d%0aX-Injected%3A+malicious could inject arbitrary additional HTTP response headers, enabling: - Session fixation via an injected Set-Cookie - Cache poisoning (injecting Location, Content-Type, etc.) - Reflected XSS in controlled response bodies -…

Published by the source

22 Apr 2026, 20:25 UTC

Last modified by the source

13 May 2026, 13:52 UTC

Source last checked

26 Oct 2026, 12:52 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-c3h8-g69v-pjrg

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-c3h8-g69v-pjrg

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# Patch Next advisory brief: CVE-2026-41683

Advisory: i18next-http-middleware: HTTP response splitting and DoS via unsanitised Content-Language header
IDs: CVE-2026-41683, GHSA-c3h8-g69v-pjrg
Record: https://patchnext.com/advisories/cve-2026-41683 (revision 2, source checked 26 Oct 2026, 12:52 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: i18next-http-middleware 3.9.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm i18next-http-middleware: affected < 3.9.3; fixed in 3.9.3

## Suggested inspection (read-only)
- `npm ls i18next-http-middleware --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on i18next-http-middleware.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-c3h8-g69v-pjrg (OSV record GHSA-c3h8-g69v-pjrg lists affected ranges: npm i18next-http-middleware >=0 <3.9.3 (fixed))
- Verified: https://github.com/advisories/GHSA-c3h8-g69v-pjrg (GitHub-reviewed advisory GHSA-c3h8-g69v-pjrg lists affected ranges: npm i18next-http-middleware >=0 <3.9.3)

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