GHSA-2933-q333-qg83 is a critical-severity (CVSS 9.1) CWE-1321 vulnerability in i18next-fs-backend. O3 Security confirms whether GHSA-2933-q333-qg83 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
i18next-fs-backend vulnerable to prototype pollution via crafted missing-key string
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-2933-q333-qg83.
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-2933-q333-qg83 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 358,265 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-fs-backendnpmDescription
Impact
i18next-fs-backend ≤ 2.6.5, when used to persist missing translation keys (e.g. via i18next-http-middleware's missingKeyHandler exposed to untrusted input), is vulnerable to prototype pollution via crafted missing-key strings.
Backend.writeFile() splits each queued missing-key string on the configured keySeparator (default .) before calling the internal setPath() walker. The walker (getLastOfPath in lib/utils.js) did not guard against unsafe segments, so a key like "__proto__.polluted" was split into ["__proto__", "polluted"] and walked straight into Object.prototype, allowing an attacker to write arbitrary properties onto the global object prototype.
Depending on the host application, polluted prototype properties may cause crashes, corrupted translation behaviour, configuration poisoning, or bypasses of property-based security checks.
Affected configuration
Applications are directly affected only if all of the following hold:
i18next-fs-backend≤ 2.6.5 is configured as the backend.i18next-http-middleware'smissingKeyHandler(or another route that forwards untrusted request bodies toi18next.t(..., { ... })withsaveMissing: true) is reachable by untrusted users.- The default behaviour of splitting missing-key strings on
keySeparatoris in use (i.e.keySeparatoris notfalse).
Apps that do not expose missing-key persistence to untrusted input are not directly affected through this attack path.
Patches
Fixed in i18next-fs-backend 2.6.6. The traversal helper now refuses to descend through __proto__, constructor, or prototype segments and drops the offending write silently. Legitimate dotted keys (e.g. "header.title") are unaffected.
A matching defence-in-depth fix has been shipped in i18next-http-middleware 3.9.7 — see the companion advisory.
Workarounds
If users cannot upgrade immediately:
- Do not expose
i18next-http-middleware'smissingKeyHandlerto untrusted users (mount it behind authentication, or remove the route). - Disable missing-key persistence (
saveMissing: false, or nobackend.createimplementation) when accepting writes from untrusted input. - Set
keySeparator: falsein the i18next options to disable backend key splitting (note: this also disables nested translation keys).
Resources
- Original report by @codeswhite.
- Companion advisory in
i18next-http-middleware: GHSA-f49m-vf83-692w. - Previous
i18next-fs-backendsecurity release: GHSA-8847-338w-5hcj (path traversal vialng/ns, fixed in 2.6.4).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | i18next-fs-backend | all versions | 2.6.6 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for i18next-fs-backend. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update i18next-fs-backend to 2.6.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-2933-q333-qg83 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 pinpoints whether GHSA-2933-q333-qg83 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-2933-q333-qg83. 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-2933-q333-qg83 in your dependencies?
O3 detects GHSA-2933-q333-qg83 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.