CVE-2026-41885

Versions of i18next-locize-backend prior to 9.0.2 interpolate lng, ns, projectId, and version directly into the configured loadPath / privatePath / addPath / updatePath / getLanguagesPath URL templates with no path-component validation and no encoding. When an application exposes any of these values to user-controlled input (?lng= / ?ns= query parameters via i18next-browser-languagedetector, cookies, request headers, or a URL-derived projectId), a crafted value can change the structure of the outgoing request URL.

Affected call sites in lib/index.js (pre-patch): the interpolate() helper is used at the five URL-build sites, _readAny/read (line 415 for private, 426 for public), getLanguages (lines 271 and 296), and writePage (lines 616 and 622) for the missing-key and update POST paths. The helper interpolate in lib/utils.js substitutes raw values with no encoding.

Related fixes shipped in 9.0.2

• The defaults() helper replaces for...in iteration with Object.keys() plus an explicit prototype-key guard so a polluted Object.prototype cannot leak into the merged options object.
• New utils.interpolateUrl / isSafeUrlSegment / sanitizeLogValue / redactUrlCredentials helpers mirror the pattern shipped in [email protected] (see its advisory GHSA-q89c-q3h5-w34g).

Affected versions

All versions of i18next-locize-backend prior to 9.0.2.

Workarounds

No workaround short of upgrading. If you cannot upgrade immediately, sanitise lng / ns / projectId / version at your application boundary before passing them through to i18next, reject values containing .., /, \, ?, #, %, whitespace, control characters, and cap the length.

Credits

Discovered via an internal security audit of the i18next / locize ecosystem.

References

• CWE-22: Path Traversal
• CWE-74: Injection
• CWE-1321: Prototype Pollution (amplification path)
• Related advisory in the same ecosystem: GHSA-q89c-q3h5-w34g (i18next-http-backend)

An attacker who can influence lng, ns, projectId, or version can:

• Path traversal, lng = '../../admin' against https://api.locize.app/{{projectId}}/{{version}}/{{lng}}/{{ns}} changes the request URL path segment that reaches the locize CDN / API.
• Query-string injection, lng = 'en?x=y' appends an attacker-chosen query to the URL.
• Fragment truncation, lng = 'en#x' silently truncates the path in browser fetches.
• URL-encoded bypass, lng = 'en%2F..' leverages server-side decoding to reintroduce /...

The worst-case concrete impact is loading an unintended translation resource (potentially causing wrong content to render) and, when a custom loadPath is configured against an internal / file-scheme URL, SSRF or arbitrary-file read on the host running the backend.

Additionally, the pre-patch interpolate() function read data[key] without excluding prototype-chain properties, under prototype-pollution conditions in the same process, that path could pull values from Object.prototype into the URL.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-41885 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (9.0.2); upgrading removes the vulnerable code path.

Kodem intelligence

Fixed in 9.0.2. lib/index.js now uses interpolateUrl() at every URL-build site and returns an error callback (or silently drops the queued write for writePage) when any interpolated value fails the safety check. Legitimate i18next language-code shapes (BCP-47, en_US, zh-Hant-HK, my-custom.ns, +-joined multi-language values) all pass.

1. What is CVE-2026-41885? CVE-2026-41885 is a medium-severity path traversal vulnerability in i18next-locize-backend (npm), affecting versions < 9.0.2. It is fixed in 9.0.2. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-41885? CVE-2026-41885 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of i18next-locize-backend are affected by CVE-2026-41885? i18next-locize-backend (npm) versions < 9.0.2 is affected.
4. Is there a fix for CVE-2026-41885? Yes. CVE-2026-41885 is fixed in 9.0.2. Upgrade to this version or later.
5. Is CVE-2026-41885 exploitable, and should I be worried? Whether CVE-2026-41885 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-41885 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-41885? Upgrade i18next-locize-backend to 9.0.2 or later.