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CVE-2026-48713— i18next-fs-backend: Prototype pollution via crafted missing-key string

Quick assessment

Affected
i18next i18next-fs-backend
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-fs-backend是i18next的后端模块组件。 i18next i18next-fs-backend 2.6.6之前版本存在输入验证错误漏洞，该漏洞源于原型污染，通过特制的缺失键字符串在持久化缺失翻译键时，可能导致攻击者向全局对象原型写入任意属性，进而导致崩溃、翻译行为错误、配置投毒或绕过基于属性的安全检查。

CVSS 9.1 · Critical EPSS 0.66% · P50

Affected Version Matrix 1

VendorProduct Version RangeStatus
i18next i18next-fs-backend < 2.6.6 affected
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I. Basic Information for CVE-2026-48713

Vulnerability Information
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Vulnerability Title
i18next-fs-backend: Prototype pollution via crafted missing-key string
Source: CVE Program / CVE List V5
Vulnerability Description
Versions prior to 2.6.6 are vulnerable to prototype pollution via crafted missing-key strings when used to persist missing translation keys (e.g. via i18next-http-middleware's missingKeyHandler exposed to untrusted input). Backend.writeFile() splits each queued missing-key string on the configured keySeparator (default .) before calling the internal setPath() walker. The walker (getLastOfPath in lib/utils.js) did not guard against unsafe segments, so a key like "__proto__.polluted" was split into ["__proto__", "polluted"] and walked straight into Object.prototype, allowing an attacker to write arbitrary properties onto the global object prototype. Depending on the host application, polluted prototype properties may cause crashes, corrupted translation behaviour, configuration poisoning, or bypasses of property-based security checks. Applications are affected only if the missingKeyHandler (or another route that forwards untrusted request bodies to i18next.t(..., { ... }) with saveMissing: true) is reachable by untrusted users and the default behaviour of splitting missing-key strings on keySeparator is in use (i.e. keySeparator is not false). Apps that do not expose missing-key persistence to untrusted input are not directly affected through this attack path. This issue has been fixed in version 2.6.6. If developers using the library are unable to upgrade immediately, they should take the following precautions: do not expose i18next-http-middleware's missingKeyHandler to untrusted users (mount it behind authentication, or remove the route), disable missing-key persistence (saveMissing: false, or no backend.create implementation) when accepting writes from untrusted input, and set keySeparator: false in their i18next options to disable backend key splitting (note: this also disables nested translation keys).
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-fs-backend 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
i18next i18next-fs-backend是i18next的后端模块组件。 i18next i18next-fs-backend 2.6.6之前版本存在输入验证错误漏洞，该漏洞源于原型污染，通过特制的缺失键字符串在持久化缺失翻译键时，可能导致攻击者向全局对象原型写入任意属性，进而导致崩溃、翻译行为错误、配置投毒或绕过基于属性的安全检查。
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-fs-backend < 2.6.6 -

II. Public POCs for CVE-2026-48713

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 11059 chars
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III. Intelligence Information for CVE-2026-48713

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Patches & Fixes for CVE-2026-48713 (1)

Vendor Advisories for CVE-2026-48713 (1)

IV. Related Vulnerabilities

Same product: i18next-fs-backend
Same vendor: i18next
Same weakness: CWE-1321

V. Comments for CVE-2026-48713

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