---
id: CVE-2026-61534
title: Yayson is a library for serializing and reading JSON API data in JavaScript
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/stor…
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H'
cwe:
  - CWE-1321
vendor: yayson
product: yayson
affected:
  - yayson <= 4.2.0
patched:
  - yayson 4.3.0
published: '2026-09-14'
updated: '2026-09-14'
sourceUpdated: '2026-09-14T20:16:48.813'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-61534'
references:
  - url: >-
      https://github.com/confetti/yayson/commit/e460162d5a3ebac86424bead7424957c36f8dff9
    label: security-advisories@github.com
  - url: 'https://github.com/confetti/yayson/pull/111'
    label: security-advisories@github.com
  - url: 'https://github.com/confetti/yayson/releases/tag/v4.3.0'
    label: security-advisories@github.com
  - url: 'https://github.com/confetti/yayson/security/advisories/GHSA-325j-mg25-8q58'
    label: security-advisories@github.com
  - url: 'https://github.com/confetti/yayson/security/advisories/GHSA-325j-mg25-8q58'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://github.com/advisories/GHSA-325j-mg25-8q58'
tags:
  - nvd
  - ghsa
  - npm
  - cve.org
  - exploit-available
aliases:
  - GHSA-325j-mg25-8q58
ecosystem: npm
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-14T19:19:38.947733Z'
ingestedAt: '2026-09-12T00:03:49.069Z'
epss: 0.00783
epssPercentile: 0.54562
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-61534)

Affected packages:

- `yayson <= 4.2.0`

Patched in:

- `yayson 4.3.0`

Source: https://github.com/advisories/GHSA-325j-mg25-8q58