Vulnerability-Lookup

CVE-2026-41683 (GCVE-0-2026-41683)

Vulnerability from cvelistv5 – Published: 2026-05-08 15:27 – Updated: 2026-05-08 23:29

Title

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

Summary

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.

Severity

8.6 (High)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-05-08 23:28 UTC

CWE

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

Assigner

GitHub_M mitre root

References

1 reference

URL	Tags
https://github.com/i18next/i18next-http-middlewar…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version	CPE status
i18next	i18next-http-middleware	Affected: < 3.9.3	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-41683

Vulnerability from fkie_nvd - Published: 2026-05-08 16:16 - Updated: 2026-06-17 10:46

Severity

8.6 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/i18next/i18next-http-middleware/security/advisories/GHSA-c3h8-g69v-pjrg

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "i18next-http-middleware",
          "vendor": "i18next",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 3.9.3"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "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 (\u003c 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(\u0027Content-Language\u0027, ...) verbatim. This issue has been patched in version 3.9.3."
    }
  ],
  "id": "CVE-2026-41683",
  "lastModified": "2026-06-17T10:46:59.900",
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          "confidentialityImpact": "LOW",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L",
          "version": "3.1"
        },
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        "impactScore": 4.7,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
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          "options": [
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  "references": [
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    }
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          "value": "CWE-79"
        },
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      "source": "security-advisories@github.com",
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}

GHSA-C3H8-G69V-PJRG

Vulnerability from github – Published: 2026-04-22 20:25 – Updated: 2026-05-13 13:29

Summary

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

Details

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+malicious could 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
Node.js ≥ 14.6.0 — denial of service. res.setHeader() throws ERR_INVALID_CHAR when 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.

Severity

8.6 (High)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "i18next-http-middleware"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.9.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-41683"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-113",
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-22T20:25:49Z",
    "nvd_published_at": "2026-05-08T16:16:11Z",
    "severity": "HIGH"
  },
  "details": "### Summary\n\nVersions 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` (\u003c 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(\u0027Content-Language\u0027, ...)` verbatim.\n\n### Impact\n\nTwo concrete outcomes depending on the Node.js version:\n\n- **Node.js \u003c 14.6.0 \u2014 HTTP response splitting.** An attacker crafting a request like `GET /?lng=en%0d%0aX-Injected%3A+malicious` could inject arbitrary additional HTTP response headers, enabling:\n  - Session fixation via an injected `Set-Cookie`\n  - Cache poisoning (injecting `Location`, `Content-Type`, etc.)\n  - Reflected XSS in controlled response bodies\n- **Node.js \u2265 14.6.0 \u2014 denial of service.** `res.setHeader()` throws `ERR_INVALID_CHAR` when 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).\n\nThe 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.\n\n### Related (same release)\n\nVersion 3.9.3 also tightens the `hasXSS()` regex that was designed as a secondary filter on detected language values. The previous pattern `/\u003c\\s*\\w+\\s*on\\w+\\s*=.*?\u003e/i` only matched event handlers in the **first** attribute position, so payloads like `\u003cinput autofocus onfocus=alert(1)\u003e` bypassed the filter. Applications that rendered `res.locals.language` into HTML with a context-unsafe templating mode (EJS `\u003c%- %\u003e`, Pug `!{\u2026}`, Handlebars `{{{\u2026}}}`) 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.\n\n### Affected versions\n\n`\u003c 3.9.3`.\n\n### Patch\n\nFixed 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.\n\n### Workarounds\n\nNo 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.\n\n### Credits\n\nDiscovered via an internal security audit of the i18next ecosystem.",
  "id": "GHSA-c3h8-g69v-pjrg",
  "modified": "2026-05-13T13:29:47Z",
  "published": "2026-04-22T20:25:49Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/i18next/i18next-http-middleware/security/advisories/GHSA-c3h8-g69v-pjrg"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-41683"
    },
    {
      "type": "WEB",
      "url": "https://github.com/i18next/i18next-http-middleware/commit/65301c194593d46a84623b64e5fde2f51d3550f6"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/i18next/i18next-http-middleware"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "i18next-http-middleware: HTTP response splitting and DoS via unsanitised Content-Language header"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-41683 (GCVE-0-2026-41683)

FKIE_CVE-2026-41683

GHSA-C3H8-G69V-PJRG

Summary

Impact

Related (same release)

Affected versions

Patch

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Sightings

Nomenclature

Related by attack behaviour