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 J…
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.
Why it matters
- ▸ Remotely exploitable over the network — no physical or local access required
- ▸ Low attack complexity — no special conditions needed to exploit
- ▸ No authentication required
- ▸ No user interaction needed — can be exploited automatically
Apply the vendor patch as soon as it's available or already released.
This analysis is generated from structured CVSS vector data, CISA KEV cross-referencing, and vendor/product category rules — not a manual expert review. Treat it as a starting point, not a substitute for your own assessment.
CVSS Vector Breakdown
EU Vulnerability Database (ENISA)
EUVD is ENISA's EU vulnerability database, still in beta. EPSS is a probabilistic exploitation-likelihood score, not a certainty.
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