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CVE-2026-61534: Product identification pending

Severity

9.1 (CRITICAL)

Affected versions

Before 4.3.0

Fixed version

4.3.0.

Patch status

Patched

Published

2026-09-14T16:17:16.847

Modified

2026-09-14T20:16:48.813

Why it matters

This matters because the affected product may allow code execution. Prioritize systems that are internet-facing or have privileged access to other infrastructure.

Recommended admin actions

• Prioritize validation immediately due to critical CVSS severity.
• Compare installed versions against the affected version range in the advisory.
• Review logs for suspicious activity related to the affected application or component.

Technical summary

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.

View the official NVD record for CVE-2026-61534

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.