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

Exploitation

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

CVSS

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

EPSS

• CVE-2026-41693: 0.29% estimated exploitation activity in the next 30 days; percentile 21.81 (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-fs-backend prior to 2.6.4 interpolate the caller-supplied lng and ns values directly into the configured loadPath and addPath templates with no path-component validation and no sanitisation. When an application exposes the resolved language code to user-controlled input (?lng= query parameter, cookie, request header), a crafted value can break out of the intended locale directory. Affected call sites in lib/index.js: - read (line 38 pre-patch): const filename = interpolate(loadPath, { lng: language, ns: namespace }) - removeFile (line 101 pre-patch): same pattern against addPath - writeFile (line 127 pre-patch): same pattern against addPath for queued missing-key writes The helper interpolate in lib/utils.js substitutes raw values with no encoding — unlike the addQueryString helper in i18next-http-backend, there is no equivalent safety for path interpolation. Impact - Arbitrary file read. With a loadPath like /locales/{{lng}}/{{ns}}.json, an…

Published by the source

22 Apr 2026, 17:43 UTC

Last modified by the source

13 May 2026, 13:50 UTC

Source last checked

26 Oct 2026, 12:52 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-8847-338w-5hcj

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-8847-338w-5hcj

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# Patch Next advisory brief: CVE-2026-41693

Advisory: i18next-fs-backend: Path traversal via unsanitised lng/ns allows arbitrary file read/overwrite
IDs: CVE-2026-41693, GHSA-8847-338w-5hcj
Record: https://patchnext.com/advisories/cve-2026-41693 (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 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: i18next-fs-backend 2.6.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm i18next-fs-backend: affected < 2.6.4; fixed in 2.6.4

## Suggested inspection (read-only)
- `npm ls i18next-fs-backend --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-fs-backend.
- 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-8847-338w-5hcj (OSV record GHSA-8847-338w-5hcj lists affected ranges: npm i18next-fs-backend >=0 <2.6.4 (fixed))
- Verified: https://github.com/advisories/GHSA-8847-338w-5hcj (GitHub-reviewed advisory GHSA-8847-338w-5hcj lists affected ranges: npm i18next-fs-backend >=0 <2.6.4)

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