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CRITICAL

CVE-2026-61534

CVSS v3

9.1

CRITICAL

EPSS Score

0.8 %

exploit probability, as of 2026-09-28

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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 supp

Technical details

Published
2026-09-14
Last Modified
2026-09-14

Frequently asked questions

What is CVE-2026-61534?

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 supp

Is CVE-2026-61534 actively exploited?

Active exploitation of CVE-2026-61534 has not been confirmed. Its EPSS score was 0.8% on 2026-09-28, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-61534?

CVE-2026-61534 has a CVSS v3 base score of 9.1 (CRITICAL severity).

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