Vulnerability in i18next-http-middleware (CVE-2026-48714)
Summary
Vulnerability in i18next-http-middleware (CVE-2026-48714). Data can be tampered with by attackers. Exploitable via missingKeyHandler. Mitigation: upgrade to 3.9.7 or later.
Original description
The description as published by the source.
i18next-http-middleware is a middleware to be used with Node.js web frameworks like express or Fastify and also for Deno. In versions prior to 3.9.7, the missingKeyHandler blocked the literal request-body keys proto, constructor, and prototype (added in 3.9.3, see GHSA-5fgg-jcpf-8jjw), but did not reject dotted variants such as "proto.polluted". Downstream backends that split the missing-key string on a configured keySeparator (notably i18next-fs-backend ≤ 2.6.5) hand these keys to an unguarded setPath() walker that writes to Object.prototype. Applications that expose missingKeyHandler to untrusted input AND use i18next-fs-backend ≤ 2.6.5 are directly exploitable for remote prototype pollution. Other downstream backends that split the missing-key string the same way may be similarly affected. Depending on the host application, polluted prototype properties may cause crashes, corrupted translation behaviour, configuration poisoning, or bypasses of property-based security checks. This issue has been fixed in version 3.9.7. If developers cannot upgrade immediately, they should do the following: do not expose missingKeyHandler to untrusted users (mount it behind authentication, or remove the route), add a request-body filter ahead of the handler that rejects any top-level key containing proto, constructor, or prototype after splitting on their configured keySeparator, and disable missing-key persistence (saveMissing: false) when accepting writes from untrusted input.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-48714 has been found in i18next-http-middleware.
Attackers can target a specific entry point like missingKeyHandler over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 9.1/10.
What to do: upgrade i18next-http-middleware to 3.9.7 or later.
If unsure, ask your IT team or search "i18next-http-middleware CVE-2026-48714" on the vendor's site.
CVE-2026-48714 (i18next-http-middleware) — CWE-1321 / CVSS v3 9.1
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: missingKeyHandler / __proto__ / constructor / prototype
Patched: 3.9.7 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-1321) exists in i18next-http-middleware. Attackers reach the vulnerable code path via missingKeyHandler without authentication.
Check the vendor advisory for the affected versions of i18next-http-middleware. Attack surface: missingKeyHandler / __proto__ / constructor / prototype.
Severity: Critical (CVSS 9.1/10). Data can be tampered with by attackers.
Update to 3.9.7.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'i18next-http-middleware' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'i18next-http-middleware' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
i18next-http-middlewareを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade i18next-http-middleware to 3.9.7ステージング環境で 3.9.7 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
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3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- patch github.com
- web github.com