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GHSA-c3h8-g69v-pjrg
No affected components available
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.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a low impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a low impact on the availability of the system.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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