Path traversal / SSRF in i18next-http-middleware via user-controlled language and namespace parameters

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

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 passes the user-controlled lng and ns values from getResourcesHandler directly into i18next.services.backendConnector.load(languages, namespaces, …) without any sanitization. Depending on which backend is configured, the unvalidated path segments enable either path traversal or SSRF. This issue has been patched in version 3.9.3.

Source published

8 May 2026 15:29:55 UTC

Source modified

8 May 2026 23:30:15 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

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 passes the user-controlled lng and ns values from getResourcesHandler directly into i18next.services.backendConnector.load(languages, namespaces, …) without any sanitization. Depending on which backend is configured, the unvalidated path segments enable either path traversal or SSRF. This issue has been patched in version 3.9.3.

Source published

May 8, 2026, 3:29:55 PM (timezone not stated)

Source modified

May 8, 2026, 11:30:15 PM (timezone not stated)

Observed here

7 Nov 2026 09:34:09 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

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

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 passes the user-controlled lng and ns values from getResourcesHandler directly into i18next.services.backendConnector.load(languages, namespaces, …) without any sanitization. Depending on which backend is configured, the unvalidated path segments enable either path traversal or SSRF. This issue has been patched in version 3.9.3.

Source published

8 May 2026 16:16:12 UTC

Source modified

26 Oct 2026 18:10:00 UTC

Observed here

27 Oct 2026 11:12:01 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

### Summary Versions of `i18next-http-middleware` prior to 3.9.3 pass the user-controlled `lng` and `ns` values from `getResourcesHandler` directly into `i18next.services.backendConnector.load(languages, namespaces, …)` without any sanitisation. Depending on which backend is configured, the unvalidated path segments enable one of two attacks: - **Filesystem path traversal** when the middleware is paired with `i18next-fs-backend` (or any backend that interpolates `lng` / `ns` into a filesystem path). - **Server-Side Request Forgery (SSRF)** when the middleware is paired with `i18next-http-backend` (or any backend that interpolates into an HTTP URL). Example request: ``` GET /locales/resources.json?lng=../../etc/passwd&ns=root ``` with `i18next-fs-backend` reads the attacker-chosen file from disk; with `i18next-http-backend` reshapes the outgoing URL to target an internal service. ### Impact - **Arbitrary file read** via `fs`-style backends — any file the Node process can read becomes reachable (source, configuration, `.ssh` keys, `.env`, Docker secrets, etc.). - **SSRF** via `http`-style backends — requests to internal IPs / hostnames not normally reachable from the internet; combined with cloud metadata endpoints this can escalate to credential theft. - **Unbounded growth of `i18next.options.ns`** — a now-incidental amplification: the pre-patch `getResourcesHandler` pushed every unique `ns` value into the shared `i18next.options.ns` singleton array without validation or bounds, enabling memory exhaustion from repeated unique payloads. The severity is bounded by the backend in place, but the middleware itself exposed the unsanitised path; this is the "weakest link" layer. ### Affected versions `< 3.9.3`. ### Patch Fixed in **3.9.3**. The patch introduces `utils.isSafeIdentifier` and applies it in `getResourcesHandler` before `lng` and `ns` reach the backend connector: ```js languages = languages.filter(utils.isSafeIdentifier) namespaces = namespaces.filter(utils.isSafeIdentifier) ``` `isSafeIdentifier` uses a denylist approach — it still accepts any legitimate i18next language-code shape ([i18next FAQ](https://www.i18next.com/how-to/faq#how-should-the-language-codes-be-formatted)) — rejecting: - `..` sequences (relative path traversal) - path separators (`/`, `\`) - control characters (C0/C1) - prototype keys (`__proto__` / `constructor` / `prototype`) - empty strings and values longer than 128 characters Unsafe values are dropped; only safe values reach the backend. The fix is a defence-in-depth layer on top of any sanitisation the backend itself may apply. ### Workarounds No workaround short of upgrading. Front-proxying the middleware with a WAF rule that rejects requests containing `..`, `/`, `\`, or URL-structure characters in `lng` / `ns` is a partial mitigation. Upgrading the configured backend (`i18next-fs-backend` ≥ 2.6.4, `i18next-http-backend` ≥ 3.0.5) also closes the same attack at the next layer. ### Related advisories fixed in the same release - [GHSA-5fgg-jcpf-8jjw](https://github.com/i18next/i18next-http-middleware/security/advisories/GHSA-5fgg-jcpf-8jjw) — prototype pollution via `setPath` and `missingKeyHandler`. Independently fixable, filed separately per CNA rules. - [GHSA-c3h8-g69v-pjrg](https://github.com/i18next/i18next-http-middleware/security/advisories/GHSA-c3h8-g69v-pjrg) — HTTP response splitting + XSS-filter bypass (CVE-2026-41683). ### Credits Discovered via an internal security audit of the i18next ecosystem. ### Resources - [CWE-22: Path Traversal](https://cwe.mitre.org/data/definitions/22.html) - [CWE-918: Server-Side Request Forgery (SSRF)](https://cwe.mitre.org/data/definitions/918.html) (specific sub-case when paired with an HTTP backend) - [i18next FAQ: language code formatting](https://www.i18next.com/how-to/faq#how-should-the-language-codes-be-formatted)

Source published

29 Apr 2026 22:26:36 UTC

Source modified

13 May 2026 13:52:33 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

Publisher rating · HIGH