HTTP response splitting and DoS in i18next-http-middleware via unsanitised Content-Language header

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Summary

CVECVE-2026-41683
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-08 16:16:11 UTC
Updated2026-05-12 15:29:40 UTC
Descriptioni18next-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.

Risk And Classification

Primary CVSS: v3.1 8.6 HIGH from [email protected]

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

EPSS: 0.000410000 probability, percentile 0.125410000 (date 2026-05-11)

Problem Types: CWE-79 | CWE-113 | CWE-79 CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') | CWE-113 CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary8.6HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L
3.1CNADECLARED8.6HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
High
Availability
Low

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA I18next I18next-http-middleware affected < 3.9.3 Not specified

References

ReferenceSourceLinkTags
github.com/i18next/i18next-http-middleware/security/advisories/GHSA-c3h8... [email protected] github.com
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