Description
Yayson is a library for serializing and reading JSON API data in JavaScript. Prior to 4.3.0, Store and LegacyStore use attacker-controlled JSON:API type, id, and relationship names as keys in plain-object lookup tables in src/yayson/store.ts and src/yayson/legacy-store.ts. A document whose type is __proto__ causes model-cache writes to modify Object.prototype, with the attacker controlling the polluted property name through id and its value through attributes. The malicious type can also be supplied by an included resource, and LegacyStore is reachable when a configured types mapping resolves to __proto__. Unsafe relationship names including __proto__, constructor, and prototype provide additional document-derived member paths. The resulting process-wide prototype pollution can cause denial of service and logic corruption; authorization bypass or code execution depends on suitable gadgets in the consuming application. This issue is fixed in version 4.3.0.
Published: 2026-09-14
Score: 9.1 Critical
EPSS: n/a
KEV: No
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Remediation

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Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-325j-mg25-8q58 yayson: Prototype pollution in Store/LegacyStore deserialization
History

Mon, 14 Sep 2026 21:00:00 +0000

Type Values Removed Values Added
Description Yayson is a library for serializing and reading JSON API data in JavaScript. Prior to 4.3.0, Store and LegacyStore use attacker-controlled JSON:API type, id, and relationship names as keys in plain-object lookup tables in src/yayson/store.ts and src/yayson/legacy-store.ts. A document whose type is __proto__ causes model-cache writes to modify Object.prototype, with the attacker controlling the polluted property name through id and its value through attributes. The malicious type can also be supplied by an included resource, and LegacyStore is reachable when a configured types mapping resolves to __proto__. Unsafe relationship names including __proto__, constructor, and prototype provide additional document-derived member paths. The resulting process-wide prototype pollution can cause denial of service and logic corruption; authorization bypass or code execution depends on suitable gadgets in the consuming application. This issue is fixed in version 4.3.0.
Title Yayson: Prototype pollution in the Store/LegacyStore deserialization
Weaknesses CWE-1321
References
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H'}

ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Subscriptions

No data.

cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-09-14T19:19:45.499Z

Reserved: 2026-07-10T16:27:03.093Z

Link: CVE-2026-61534

cve-icon Vulnrichment

Updated: 2026-09-14T19:19:10.572Z

cve-icon NVD

Status : Received

Published: 2026-09-14T16:17:16.847

Modified: 2026-09-14T20:16:48.813

Link: CVE-2026-61534

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses