i18next i18next-http-backend up to 3.0.4 Control Character path traversal

Summaryinfo

A vulnerability marked as critical has been reported in i18next i18next-http-backend up to 3.0.4. This issue affects some unknown processing of the component Control Character Handler. This manipulation causes path traversal. This vulnerability is handled as CVE-2026-41691. The attack can be initiated remotely. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability classified as critical was found in i18next i18next-http-backend up to 3.0.4. Affected by this vulnerability is an unknown code of the component Control Character Handler. The manipulation with an unknown input leads to a path traversal vulnerability. The CWE definition for the vulnerability is CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Copilot said: i18nextify is a JavaScript library that adds i18nextify is a JavaScript library that adds website internationalization via a script tag, without source code changes. Versions prior to 3.0.5 interpolate the lng and ns values directly into the configured loadPath / addPath URL template without any encoding, validation, or path sanitisation. When an application exposes the language-code selection to user-controlled input (the default — i18next-browser-languagedetector reads ?lng= query params, cookies, localStorage, and request headers), an attacker can inject characters that change the structure of the outgoing request URL. This is a single URL-injection vulnerability. The attacker-controlled value is neutralised before it is used as part of an output URL string; the attack shape covers both path traversal and broader URL-structure injection — both are closed by the one interpolateUrl sanitisation fix. This issue has been fixed in version 3.0.5. If users cannot upgrade immediately, they can work around the issue by sanitising lng / ns before they reach i18next (strip .., /, \, ?, #, %, whitespace, and control characters; cap the length).

The advisory is shared at github.com. This vulnerability is known as CVE-2026-41691 since 04/22/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1006 for this issue.

Upgrading to version 3.0.5 eliminates this vulnerability. Applying the patch 4cee84f229c637b9c182366d3156f726d407a621 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

• i18next

Name

• i18next-http-backend

Version

• 3.0.0
• 3.0.1
• 3.0.2
• 3.0.3
• 3.0.4

License

• open-source

Website

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

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