GHSA-c3h8-g69v-pjrg is a high-severity (CVSS 8.6) vulnerability in i18next-http-middleware. O3 Security confirms whether GHSA-c3h8-g69v-pjrg is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
i18next-http-middleware: HTTP response splitting and DoS via unsanitised Content-Language header
Real-World Exposure
i18next-http-middlewareReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Versions of i18next-http-middleware prior to 3.9.3 wrote user-controlled language values into the Content-Language response header after passing them through utils.escape(), which is an HTML-entity encoder that does not strip carriage return, line feed, or other control characters. When the application used an older i18next (< 19.5.0) that still exercised the backward-compatibility fallback at LanguageDetector.js:100 or otherwise produced a raw detected value, CRLF sequences in the attacker-controlled lng parameter reached res.setHeader('Content-Language', ...) verbatim.
Impact
Two concrete outcomes depending on the Node.js version:
- Node.js < 14.6.0 — HTTP response splitting. An attacker crafting a request like
GET /?lng=en%0d%0aX-Injected%3A+maliciouscould inject arbitrary additional HTTP response headers, enabling:- Session fixation via an injected
Set-Cookie - Cache poisoning (injecting
Location,Content-Type, etc.) - Reflected XSS in controlled response bodies
- Session fixation via an injected
- Node.js ≥ 14.6.0 — denial of service.
res.setHeader()throwsERR_INVALID_CHARwhen the value contains CRLF. Because the middleware did not catch this error, it propagated as an unhandled exception, returning a 500 response to all concurrent users sharing that process (in worker-pool deployments this can knock out a full server instance).
The same header-setting code path fires inside the languageChanged event listener and again in the main middleware flow, so the flaw was triggered at least twice per affected request.
Related (same release)
Version 3.9.3 also tightens the hasXSS() regex that was designed as a secondary filter on detected language values. The previous pattern /<\s*\w+\s*on\w+\s*=.*?>/i only matched event handlers in the first attribute position, so payloads like <input autofocus onfocus=alert(1)> bypassed the filter. Applications that rendered res.locals.language into HTML with a context-unsafe templating mode (EJS <%- %>, Pug !{…}, Handlebars {{{…}}}) could be XSSed despite the filter being in place. This bypass is noted here because it is fixed in the same release, but the primary vulnerability reported in this advisory is the CRLF/header-injection path above.
Affected versions
< 3.9.3.
Patch
Fixed in 3.9.3. The patch introduces utils.sanitizeHeaderValue(str) which strips \r, \n, and other C0/C1 control characters, and replaces both utils.escape(lng) call sites in lib/index.js with it. The hasXSS() regex has also been tightened to match event-handler attributes at any position.
Workarounds
No workaround short of upgrading. Front-proxying the middleware with a WAF rule that rejects \r/\n in query parameters, cookies, and path segments 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 | 3.9.3 |
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. 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-http-middleware to 3.9.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-c3h8-g69v-pjrg 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-c3h8-g69v-pjrg 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-c3h8-g69v-pjrg. 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-c3h8-g69v-pjrg in your dependencies?
O3 detects GHSA-c3h8-g69v-pjrg across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.