# CVE-2026-41683: HTTP response splitting and DoS in i18next-http-middleware via unsanitised Content-Language header

> Attackers can inject CRLF sequences into HTTP headers causing response splitting and denial of service in Node.js applications using vulnerable i18next middleware.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 May 2026
- **Updated:** 8 May 2026
- **Also known as:** GHSA-c3h8-g69v-pjrg

## What is CVE-2026-41683?

CVE-2026-41683 is a high-severity vulnerability in i18next-http-middleware, published on 8 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-113 (Improper Neutralization of CRLF Sequences in HTTP Headers)

## Which versions are affected by CVE-2026-41683?

2 open source packages ship an affected version, including i18next-http-middleware.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `i18next-http-middleware` | npm | All versions | 3.9.3 |
| `i18next-http-middleware` | npm | All versions | 3.9.3 |

## How do I fix CVE-2026-41683?

Upgrade i18next-http-middleware to 3.9.3 or later.

## Is CVE-2026-41683 being exploited?

There is no known exploitation of CVE-2026-41683 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-41683 and fix it if it is affected.

What it is: CVE-2026-41683 is a high-severity vulnerability in i18next-http-middleware, published on 8 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-41683 in the wild and no public exploit code.

Affected packages and fixed versions:
- i18next-http-middleware (npm): affected all versions; fixed in 3.9.3
- i18next-http-middleware (npm): affected all versions; fixed in 3.9.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-41683/ (Markdown: https://insights.sbomify.com/CVE-2026-41683/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-41683
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-41683
- OSV: https://osv.dev/vulnerability/CVE-2026-41683

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-41683/
Summaries are generated and may contain mistakes; the official description above is the record.