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CVE-2026-48714— i18next-http-middleware missingKeyHandler does not reject keys whose segments contain prototype-polluting names

Quick assessment

Affected
i18next i18next-http-middleware
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

i18next i18next-http-middleware是i18next的Web中间件。 i18next i18next-http-middleware 3.9.7之前版本存在输入验证错误漏洞，该漏洞源于missingKeyHandler对请求体键的清理不足，未能拒绝带点的变体键（如“__proto__.polluted”），导致下游后端（如i18next-fs-backend 2.6.5及之前版本）的未受保护的setPath()可写入Object.prototype，从而导致远程原型污染，攻击者可

CVSS 9.1 · Critical EPSS 0.66% · P50

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
i18next i18next-http-middleware < 3.9.7 affected
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I. Basic Information for CVE-2026-48714

Vulnerability Information
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Vulnerability Title
i18next-http-middleware missingKeyHandler does not reject keys whose segments contain prototype-polluting names
Source: CVE Program / CVE List V5
Vulnerability Description
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: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
CWE-1321
Source: CVE Program / CVE List V5
Vulnerability Title
i18next i18next-http-middleware 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
i18next i18next-http-middleware是i18next的Web中间件。 i18next i18next-http-middleware 3.9.7之前版本存在输入验证错误漏洞，该漏洞源于missingKeyHandler对请求体键的清理不足，未能拒绝带点的变体键（如“__proto__.polluted”），导致下游后端（如i18next-fs-backend 2.6.5及之前版本）的未受保护的setPath()可写入Object.prototype，从而导致远程原型污染，攻击者可
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
i18next i18next-http-middleware < 3.9.7 -

II. Public POCs for CVE-2026-48714

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 7645 chars
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III. Intelligence Information for CVE-2026-48714

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Patches & Fixes for CVE-2026-48714 (1)

Vendor Advisories for CVE-2026-48714 (1)

IV. Related Vulnerabilities

Same product: i18next-http-middleware
Same vendor: i18next
Same weakness: CWE-1321

V. Comments for CVE-2026-48714

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