How severe is CVE-2026-42353?

CVE-2026-42353 has a CVSS score of 8.2/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-42353?

CVE-2026-42353 affects the following packages: i18next-http-middleware (npm). Ecosystems affected: npm.

How do I fix CVE-2026-42353?

Update i18next-http-middleware to 3.9.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42353 is resolved across your whole dependency graph.

How do I detect CVE-2026-42353 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for i18next-http-middleware, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-42353 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2026-42353 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-42353 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-42353?

CVE-2026-42353 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 32th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-42353?

CVE-2026-42353 is classified as Path Traversal (CWE-22), Server-Side Request Forgery (SSRF) (CWE-918). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-42353 published, and has it been updated?

CVE-2026-42353 was published on May 8, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

HIGH severity

CVE-2026-42353 — i18next-http-middleware

HIGH

CVE-2026-42353 is a high-severity (CVSS 8.2) Path Traversal vulnerability in i18next-http-middleware. A fix is available for i18next-http-middleware — see the affected versions and patch details below.

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

Also known asGHSA-jfgf-83c5-2c4m

Published

May 8, 2026

Updated

Oct 21, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 25, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42353.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk-0.05%

Lower risk than most CVEs32th percentile — riskier than 32% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

79other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

i18next-http-middlewarenpm

164Kdownloads / week

Description

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:

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) — 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 — prototype pollution via setPath and missingKeyHandler. Independently fixable, filed separately per CNA rules.
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
CWE-918: Server-Side Request Forgery (SSRF) (specific sub-case when paired with an HTTP backend)
i18next FAQ: language code formatting

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`i18next-http-middleware`	all versions	3.9.3`npm install i18next-http-middleware@3.9.3`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for i18next-http-middleware, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update i18next-http-middleware to 3.9.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42353 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

### 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-bac