i18next-http-backend has Path Traversal & URL Injection via Unsanitised lng/ns

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.

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).

Source published

7 May 2026 20:09:24 UTC

Source modified

8 May 2026 13:08:58 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

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).

Source published

May 7, 2026, 8:09:24 PM (timezone not stated)

Source modified

May 8, 2026, 1:08:58 PM (timezone not stated)

Observed here

1 Nov 2026 07:10:42 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 3.1 · 6.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

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).

Source published

7 May 2026 21:16:29 UTC

Source modified

26 Oct 2026 20:10:00 UTC

Observed here

27 Oct 2026 10:10:19 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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

CVSS 3.1 · [email protected] · Primary · 9.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

### Summary Versions of `i18next-http-backend` 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. Affected call sites: - `_readAny` — `lib/index.js:64`: `interpolate(resolvedLoadPath, { lng: languages.join('+'), ns: namespaces.join('+') })` - `create` — `lib/index.js:123` (pre-patch): `interpolate(addPath, { lng, ns: namespace })` The helper `interpolate` (`lib/utils.js`) previously returned the raw value with no encoding. In contrast, `addQueryString` already correctly uses `encodeURIComponent` for each query-string param — only the URL-path substitution was unprotected. ### Impact An attacker who can influence the resolved `lng` or `ns` value can alter the URL in several ways: - **Path traversal** — `lng = '../../config'` turns `/locales/{{lng}}/{{ns}}.json` into `/locales/../../config/translation.json`. On a misconfigured web server, this can cause the request to target a different resource than intended; in SSR pipelines that use `file://` or similar schemes for `loadPath`, it can read arbitrary files from the host filesystem. - **Query-string injection** — `lng = 'en?admin=true'` turns `/locales/{{lng}}/{{ns}}.json` into `/locales/en?admin=true/translation.json`. Some server frameworks parse the query portion with higher priority than the path and branch on attacker-controlled flags. - **Fragment truncation** — `lng = 'en#anything'` silently discards the rest of the path in browser fetches (client cannot see the final URL). - **URL-encoded bypasses** — `lng = 'en%2F..'`, after server-side URL decoding, resolves to `en/..` — the attacker bypasses the absence of a literal `/` in their input. The practical worst case is **SSRF** when `loadPath` is an internal or file-scheme URL, and **path-based authorisation bypass** against servers that segment access by URL prefix. ### Also fixed in 3.0.5 - **Per-instance `omitFetchOptions`.** A module-level boolean in `lib/request.js` was flipped to `true` the first time any backend instance hit a "not implemented" fetch error. Once flipped, **all** subsequent requests from **all** backend instances in the same module silently stripped every user-configured fetch option — including security-relevant `credentials`, `mode`, and `cache`. One misbehaving instance (for example during SSR hydration or in React Native) permanently removed these protections process-wide. 3.0.5 scopes the flag to the backend's `options` object (`options._omitFetchOptions`) so one instance's fallback cannot pollute siblings. - **Log forging via control characters in `lng`/`ns`.** Error callbacks embedded the raw `lng`/`ns`/URL in the message string. Crafted CR/LF values could inject fake log lines into file-backed log aggregators (CWE-117). 3.0.5 strips C0/C1 control chars before concatenation. - **Basic-auth credentials leaked into error callbacks.** If `loadPath` contained a `user:password@host` authority, the full URL (including the credentials) ended up in the error message strings returned to the caller. 3.0.5 redacts `user:password@` before logging. - **Prototype-pollution amplification via `for...in`.** `addQueryString` and the XHR `customHeaders` loop used `for...in` which walks the prototype chain. Polluted `Object.prototype` entries could leak into URL query parameters and request headers. 3.0.5 uses `Object.keys` and an explicit prototype-key guard. ### Affected versions All versions of `i18next-http-backend` prior to **3.0.5**. ### Patch Fixed in **3.0.5**. Summary of the hardening: 1. New `utils.interpolateUrl` (used by `_readAny` and `create`) returns `null` if any substitution fails the URL-segment safety check (blocks `..`, `/`, `\`, `?`, `#`, `%`, `@`, whitespace, control chars, prototype keys, and values > 128 chars). Multi-language joins (`en+de`) are validated per-segment. The call sites now refuse to issue a request when the check fails and call back with a clear error. 2. `omitFetchOptions` is stored per-instance on `options._omitFetchOptions`. 3. Error-callback messages sanitise strings and redact URL credentials. 4. `for...in` over untrusted objects replaced with `Object.keys` + prototype-key guard. ### Workarounds No workaround short of upgrading. If you cannot upgrade immediately, sanitise `lng` / `ns` yourself before they reach i18next (strip `..`, `/`, `\`, `?`, `#`, `%`, whitespace, and control characters; cap the length). ### Credits Discovered via an internal security audit of the i18next ecosystem.

Source published

22 Apr 2026 17:41:24 UTC

Source modified

11 May 2026 13:53:06 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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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:L/I:L/A:N

Publisher rating · MODERATE