GHSA-5fgg-jcpf-8jjw — i18next-http-middleware
HIGHGHSA-5fgg-jcpf-8jjw is a high-severity (CVSS 8.6) Path Traversal vulnerability in i18next-http-middleware. A fix is available for i18next-http-middleware — see the affected versions and patch details below.
i18next-http-middleware: Prototype pollution and path traversal via user-controlled language and namespace parameters
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 GHSA-5fgg-jcpf-8jjw.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-5fgg-jcpf-8jjw plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 376,715 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
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.
i18next-http-middlewarenpmDescription
Summary
Versions of i18next-http-middleware prior to 3.9.3 pass user-controlled lng and ns parameters to two internal paths that use them in ways that enable prototype pollution and, depending on the configured backend, path traversal or SSRF.
The vulnerable entry points are unauthenticated HTTP handlers that are part of the middleware's public API:
getResourcesHandler— readslng/nsfrom query parameters or route params and passes them unvalidated to:utils.setPath(resources, [lng, ns], ...)— thesetPathhelper did not guard against__proto__,constructor, orprototypekeys, writing intoObject.prototypewhen those values were supplied.i18next.services.backendConnector.load(languages, namespaces, ...)— depending on the configured backend, unvalidated path segments enabled filesystem path traversal (e.g. withi18next-fs-backend) or SSRF (e.g. withi18next-http-backend).- A
namespaces.forEach(ns => i18next.options.ns.push(ns))loop additionally performed permanent, unbounded growth of the shared singleton namespace list.
missingKeyHandler— iterated the incoming request body withfor...in, which traverses inherited prototype-chain properties. A POST body like{"__proto__": {"isAdmin": true}}was forwarded intosaveMissing.
Impact
- Prototype pollution — a single unauthenticated request of the form
GET /locales/resources.json?lng=__proto__&ns=isAdminwrites intoObject.prototype, affecting every plain object created subsequently in the Node.js process. This can break authorization checks (if (user.isAdmin)), cause denial of service via type confusion, or be chained into RCE depending on what downstream code reads from polluted objects. - Path traversal / SSRF — with filesystem or HTTP backends that interpolate
lng/nsinto paths or URLs, attacker-controlled values likens=../../etc/passwdorlng=internal-servicecould reach resources outside the intended scope. - Denial of service — the unbounded
i18next.options.nsgrowth, plus repeated backend load calls, enabled memory and CPU exhaustion from unique namespace payloads.
Affected versions
< 3.9.3.
Patch
Fixed in 3.9.3. The patch:
- Blocks
__proto__,constructor, andprototypekeys inutils.setPath. - Replaces the
for...inbody iteration inmissingKeyHandlerwithObject.keys()plus an explicit dangerous-keys guard. - Introduces a
utils.isSafeIdentifierhelper (denylist approach — still permits any legitimate i18next language code shape) that filterslng/nsvalues for path-traversal, path separators, control characters, prototype keys, and over-long inputs before they reach the backend connector and before they are pushed intoi18next.options.ns.
Workarounds
No workaround short of upgrading. Front-proxying the middleware with a WAF rule that rejects requests containing __proto__, constructor, prototype, .., or control characters in lng/ns query parameters or body keys is a partial mitigation.
Credits
Discovered via an internal security audit of the i18next ecosystem.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | i18next-http-middleware | all versions | 3.9.3npm install i18next-http-middleware@3.9.3 |
Detection & mitigation playbook
Open-source dependencyDetect
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 GHSA-5fgg-jcpf-8jjw is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-5fgg-jcpf-8jjw can be triaged on real exposure rather than presence alone.
Tailored to GHSA-5fgg-jcpf-8jjw. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-5fgg-jcpf-8jjw in your dependencies?
O3 Security finds GHSA-5fgg-jcpf-8jjw across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.