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

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.

Scores

EPSS (exploitation in 30 days)

0.33% · top 74% of all CVEs (6 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: yes · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.6.

Weakness

• CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (opens in a new tab)All about CWE-79 and its CVEs
• CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') (opens in a new tab)All about CWE-113 and its CVEs

Affected products

• i18next · i18next-http-middleware

  • affected < 3.9.3

Affected packages

From reviewed advisories of the GitHub Advisory Database.

• npmi18next-http-middlewareGHSA-c3h8-g69v-pjrg (opens in a new tab)

References (1)

• https://github.com/i18next/i18next-http-middleware/security/advisories/GHSA-c3h8-g69v-pjrg (opens in a new tab)x_refsource_CONFIRM

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisory GHSA-c3h8-g69v-pjrg (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-41683](https://trackcve.app/badge/CVE-2026-41683.svg)](https://trackcve.app/cve/CVE-2026-41683)

Record last updated 8 May 2026, 23:29 UTC.