What is the CVSS score of CVE-2026-42353?

CVE-2026-42353 has a CVSS 3.1 base score of 8.2 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N. EPSS exploitation probability: 0.1%.

Which versions of i18next-http-middleware are affected by CVE-2026-42353?

i18next-http-middleware before version 3.9.3 is vulnerable to file-read and internal-access attacks that could expose credentials and configuration files.. A patch is available.

How to fix or mitigate CVE-2026-42353?

Within 24 hours, identify all systems running i18next-http-middleware and assess what sensitive files or internal services would be exposed if exploited. Within 7 days, test and deploy i18next-http-middleware version 3.9.3 to all production systems, starting with the highest-risk environments. Within 30 days, confirm all instances have been upgraded through automated dependency scanning and review application logs for any unexpected access attempts to the getResourcesHandler endpoint.

i18next-http-middleware CVE-2026-42353

HIGH

Path Traversal (CWE-22)

2026-04-29 https://github.com/i18next/i18next-http-middleware

GHSA-jfgf-83c5-2c4m

XSS Docker Path Traversal SSRF

8.2

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

8.2 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

vuln.today AI

6.5 MEDIUM

Remote unauthenticated (AV:N/PR:N/UI:N), but AC:H because it requires a specific backend and the resource handler mounted; C:H for arbitrary file read, A:L for ns memory exhaustion, no integrity impact.

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

4.0 AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

Low

Availability

None

Lifecycle Timeline

Source Code Evidence Fetched

Jul 24, 2026 - 01:21 vuln.today

Analysis Generated

Jul 24, 2026 - 01:21 vuln.today

CVE Published

Apr 29, 2026 - 22:26 nvd

HIGH 8.2

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

1 npm packages depend on i18next-http-middleware (1 direct, 0 indirect)

Ecosystem-wide dependent count for version 3.9.3.

DescriptionGitHub Advisory

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

AnalysisAI

Arbitrary file read and Server-Side Request Forgery in i18next-http-middleware before 3.9.3 arise because the getResourcesHandler route passes user-controlled 'lng' and 'ns' query parameters straight into i18next's backendConnector.load() with no sanitisation, letting attackers inject path-traversal or URL-shaping payloads through the resource-loading endpoint. The concrete impact depends on the paired backend: with i18next-fs-backend it becomes arbitrary filesystem read (e.g. /etc/passwd, .env, .ssh keys, Docker secrets), and with i18next-http-backend it becomes SSRF against internal services and cloud metadata endpoints. No public exploit identified at time of analysis and EPSS is very low (0.05%), but a working example request is documented in the vendor advisory and a fixed release (3.9.3) is available.

Technical ContextAI

i18next is a widely used JavaScript internationalization framework; i18next-http-middleware is its Express/Connect-style middleware that, among other things, exposes getResourcesHandler to serve translation resources over HTTP. The vulnerable code forwards the raw 'lng' (language) and 'ns' (namespace) request values into i18next.services.backendConnector.load(languages, namespaces, …). Because pluggable backends interpolate those tokens into a resource locator, the flaw is a classic CWE-22 (Improper Limitation of a Pathname to a Restricted Directory / Path Traversal): with a filesystem backend the tokens become path segments, and with an HTTP backend the same untrusted tokens become part of an outbound URL, producing the CWE-918 SSRF sub-case. The CPE identifies the single affected package pkg:npm/i18next-http-middleware; the actual reachable impact is a property of the configured backend (i18next-fs-backend vs i18next-http-backend), which is why the advisory calls the middleware the 'weakest link' layer.

RemediationAI

Vendor-released patch: 3.9.3 - upgrade i18next-http-middleware to 3.9.3 or later, which adds utils.isSafeIdentifier and filters 'lng'/'ns' (rejecting '..' sequences, path separators, control characters, prototype keys, empty strings, and values over 128 characters) before they reach the backend connector. There is no full workaround short of upgrading; as a partial compensating control, front the middleware with a WAF/reverse-proxy rule that rejects requests whose 'lng' or 'ns' parameters contain '..', '/', '\', or URL-structure characters (trade-off: denylist rules can be bypassed with encoding tricks and may block unusual-but-legitimate locale codes). As defence-in-depth at the next layer, also upgrade the configured backend to i18next-fs-backend ≥ 2.6.4 or i18next-http-backend ≥ 3.0.5, which close the same class of abuse. Advisory: https://github.com/i18next/i18next-http-middleware/security/advisories/GHSA-jfgf-83c5-2c4m.