CVE-2026-41693

i18next-fs-backend: Path traversal via unsanitised lng/ns allows arbitrary file read/overwrite

• Arbitrary file read. With a loadPath like /locales/{{lng}}/{{ns}}.json, an attacker-controlled lng = '../../etc' (and matching ns) causes the backend to read a file outside the locale directory. For parsers that tolerate arbitrary content (YAML's freeform text), the file contents surface as a translation resource.
• Arbitrary file overwrite. addPath is interpolated the same way for missing-key writes (the create() code path and the debounced writer in writeFile). A traversing lng/ns combination can cause the process to write JSON structures to an unintended filesystem location, potentially overwriting application files if the process user has write access.
• Chain with .js/.ts eval. i18next-fs-backend supports loading .js and .ts locale files by eval-ing their content (intentional feature, documented as requiring trusted sources). Combining traversal with that path, for example lng = '../../../app/config' against loadPath: '/locales/{{lng}}/{{ns}}.js', would cause the backend to execute a server-side file as JavaScript, exfiltrating whatever it can touch (process.env, connected services).

Exploitation requires the application to pass an untrusted lng/ns value through to i18next.t() without its own validation. Many i18next setups do exactly this via i18next-browser-languagedetector (query string / cookie detection).

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-2026-41693 has a CVSS score of 8.2 (High). 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 (2.6.4); upgrading removes the vulnerable code path.

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Fixed in 2.6.4. lib/utils.js now exports:

• isSafePathSegment(v), returns true only if v is a non-empty string of ≤ 128 chars that does not contain .., /, \, control characters, or a prototype key (__proto__, constructor, prototype). Legitimate i18next language-code shapes (BCP-47, en_US, zh-Hant-HK, pirate-speak, my-custom.ns, +-joined multi-language values) all pass.
• interpolatePath(template, data), substitutes variables like the existing interpolate but refuses the whole result if any segment fails isSafePathSegment. Callers bail out with an error (read) or silently drop the queued write (writeFile, removeFile).

The .js / .ts eval behaviour is intentionally retained, dynamic expressions in locale files are a documented feature of this backend, and safe replacements like dynamic import() are async-only and incompatible with this backend's sync-capable code path. The README has a new "Security considerations" section that spells out the trust model: .js/.ts locale files must be treated as code.

1. What is CVE-2026-41693? CVE-2026-41693 is a high-severity path traversal vulnerability in i18next-fs-backend (npm), affecting versions < 2.6.4. It is fixed in 2.6.4. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-41693? CVE-2026-41693 has a CVSS score of 8.2 (High). 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-fs-backend are affected by CVE-2026-41693? i18next-fs-backend (npm) versions < 2.6.4 is affected.
4. Is there a fix for CVE-2026-41693? Yes. CVE-2026-41693 is fixed in 2.6.4. Upgrade to this version or later.
5. Is CVE-2026-41693 exploitable, and should I be worried? Whether CVE-2026-41693 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-2026-41693 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-2026-41693? Upgrade i18next-fs-backend to 2.6.4 or later.

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