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CVE-2026-63402— i18next: Shared built-in corruption through inherited-key deepExtend recursion

Quick assessment

Affected
i18next i18next
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

i18next 是一个用于 JavaScript 的国际化（i18n）框架。在 26.3.4 版本之前， 中的 函数使用 运算符检查属性是否存在，并会递归遍历通过 继承的内置对象。若应用程序显式地将攻击者控制的数据传递给 ，且同时设置 和 ，则攻击者可利用如 、 和 等源键，选中共享的继承自内置函数对象，并通过嵌套值覆盖这些对象在全局范围内的属性。例如，将 设置为不可调用，会导致后续所有调用（包括 i18next 内部机制）抛出 ，从而引发不可恢复的服务拒绝（DoS），并造成有限的数据完整性影响。现有的 / 防护机

CVSS 5.9 · Medium
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I. Basic Information for CVE-2026-63402

Vulnerability Information
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Vulnerability Title
i18next: Shared built-in corruption through inherited-key deepExtend recursion
Source: CVE Program / CVE List V5
Vulnerability Description
i18next is an internationalization framework for JavaScript. Prior to version 26.3.4, `deepExtend` in `src/utils.js` checks property existence with the in operator and recurses into inherited built-ins reached through `Object.prototype`. An application must explicitly pass attacker-controlled resource data to `addResourceBundle(lng, ns, data, deep, overwrite)` with both `deep: true` and `overwrite: true`. Source keys such as `hasOwnProperty`, `toString` and `valueOf` can then select shared inherited built-in function objects, and a nested value can overwrite a property of those objects process-wide. For example, making `Object.prototype.hasOwnProperty.call` non-callable causes subsequent uses, including i18next internals, to throw TypeError, resulting in unrecoverable denial of service and limited integrity impact. The `__proto__`/`constructor` guard does not prevent this mechanism because the corruption target is an inherited built-in function rather than the prototype object itself. Default calls without deep merging or with overwrite falsy are unaffected, and no standard i18next backend or integration uses the vulnerable configuration. This issue is distinct from the setPath/key-walking prototype-pollution flaws in i18next-fs-backend (CVE-2026-48713) and i18next-http-middleware (CVE-2026-48714). This issue is fixed in version 26.3.4.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
对假设不可变数据的修改(MAID)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
i18next i18next < 26.3.4 -

II. Public POCs for CVE-2026-63402

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III. Intelligence Information for CVE-2026-63402

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Other References for CVE-2026-63402 (3)

IV. Related Vulnerabilities

Same vendor: i18next
Same weakness: CWE-471