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.
Published: 2026-10-30
Score: 5.9 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
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Remediation

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History

Fri, 06 Nov 2026 00:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-915
References
Metrics threat_severity

None

threat_severity

Moderate


Thu, 05 Nov 2026 03:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 30 Oct 2026 23:45:00 +0000

Type Values Removed Values Added
First Time appeared I18next
I18next i18next
Vendors & Products I18next
I18next i18next

Fri, 30 Oct 2026 22:45:00 +0000

Type Values Removed Values Added
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.
Title i18next: Shared built-in corruption through inherited-key deepExtend recursion
Weaknesses CWE-1321
CWE-471
References
Metrics cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-11-05T03:00:11.398Z

Reserved: 2026-07-16T19:20:28.987Z

Link: CVE-2026-63402

cve-icon Vulnrichment

Updated: 2026-11-05T03:00:05.108Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-30T23:17:15.400

Modified: 2026-11-05T03:17:30.993

Link: CVE-2026-63402

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-10-30T22:39:07Z

Links: CVE-2026-63402 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-11-06T02:30:14Z

Weaknesses