i18next i18next-http-middleware up to 3.9.2 Response Header utils.escape lng cross site scripting

Summaryinfo

A vulnerability was found in i18next i18next-http-middleware up to 3.9.2. It has been declared as problematic. This affects the function utils.escape of the component Response Header Handler. The manipulation of the argument lng results in cross site scripting. This vulnerability was named CVE-2026-41683. The attack may be performed from remote. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in i18next i18next-http-middleware up to 3.9.2. Affected is the function utils.escape of the component Response Header Handler. The manipulation of the argument lng with an unknown input leads to a cross site scripting vulnerability. CWE is classifying the issue as CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. This is going to have an impact on integrity. CVE summarizes:

i18next-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.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-41683 since 04/22/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Successful exploitation requires user interaction by the victim. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1059.007 by the MITRE ATT&CK project.

Upgrading to version 3.9.3 eliminates this vulnerability.

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Productinfo

Type

• Middleware

Vendor

• i18next

Name

• i18next-http-middleware

Version

• 3.9.0
• 3.9.1
• 3.9.2

Website

• Product: https://github.com/i18next/i18next-http-middleware/

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