CVE-2026-61534 (GCVE-0-2026-61534)

Vulnerability from cvelistv5 – Published: 2026-09-14 15:36 – Updated: 2026-09-14 19:19

Title

Yayson: Prototype pollution in the Store/LegacyStore deserialization

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.

Severity

9.1 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

SSVC

Exploitation: poc Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-14 19:19 UTC

CWE

CWE-1321 - Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/confetti/yayson/security/advis…	x_refsource_CONFIRM
https://github.com/confetti/yayson/pull/111	x_refsource_MISC
https://github.com/confetti/yayson/commit/e460162…	x_refsource_MISC
https://github.com/confetti/yayson/releases/tag/v4.3.0	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
confetti	yayson	Affected: < 4.3.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-61534

Vulnerability from fkie_nvd - Published: 2026-09-14 16:17 - Updated: 2026-09-14 20:16

Severity

9.1 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/confetti/yayson/commit/e460162d5a3ebac86424bead7424957c36f8dff9
	security-advisories@github.com	https://github.com/confetti/yayson/pull/111
	security-advisories@github.com	https://github.com/confetti/yayson/releases/tag/v4.3.0
	security-advisories@github.com	https://github.com/confetti/yayson/security/advisories/GHSA-325j-mg25-8q58
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/confetti/yayson/security/advisories/GHSA-325j-mg25-8q58

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "yayson",
          "vendor": "confetti",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 4.3.0"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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."
    }
  ],
  "id": "CVE-2026-61534",
  "lastModified": "2026-09-14T20:16:48.813",
  "metrics": {
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        "cvssData": {
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          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 9.1,
          "baseSeverity": "CRITICAL",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
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          "version": "3.1"
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        "impactScore": 5.2,
        "source": "security-advisories@github.com",
        "type": "Secondary"
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GHSA-325J-MG25-8Q58

Vulnerability from github – Published: 2026-09-11 22:11 – Updated: 2026-09-11 22:11

Summary

yayson: Prototype pollution in Store/LegacyStore deserialization

Details

Summary

Store/LegacyStore key internal lookup tables by the type, id, and relationship names from a JSON:API document. Because these were plain objects, a document with type: "__proto__" writes onto Object.prototype, polluting every object in the process.

Severity

Suggested CVSS v3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H (8.1). The guaranteed impact is process-wide DoS / logic corruption; escalation to authorization bypass or RCE is dependent on gadgets in the consuming application.

Affected / Patched

Affected: <= 4.2.0 (verified in 3.0.0 and 4.2.0; all 3.x and 4.x).
Patched: 4.3.0.

Details

type is a string value, untouched by JSON.parse, and is used directly as an object key:

if (!models[type]) models[type] = {}          // models["__proto__"] is Object.prototype → skipped
if (!models[type][id]) models[type][id] = model // → Object.prototype[id] = model

The attacker controls the polluted key (id) and value (the model, populated from attributes). Pollution persists for the process lifetime. The malicious type can also arrive via an included resource referenced by a relationship, bypassing any data.type allow-list. LegacyStore is additionally reachable when a configured types mapping resolves to "__proto__".

Proof of concept

const { Store } = require('yayson')()
new Store().sync({ data: { type: '__proto__', id: 'polluted', attributes: { x: 1 } } })
console.log(({}).polluted) // { x: 1, id: 'polluted' }  ← Object.prototype polluted

Workarounds

Reject documents whose type or relationship names are __proto__, constructor, or prototype, or run Node with --disable-proto=throw.

Fix

Null-prototype lookup tables, rejection of __proto__/constructor/prototype as document-derived member names, Object.keys() iteration, and null-prototype normalization of caller-supplied caches.

Severity

9.1 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.2.0"
      },
      "package": {
        "ecosystem": "npm",
        "name": "yayson"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.3.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-61534"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1321"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-11T22:11:38Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "# Summary\n`Store`/`LegacyStore` key internal lookup tables by the `type`, `id`, and relationship names from a JSON:API document. Because these were plain objects, a document with `type: \"__proto__\"` writes onto `Object.prototype`, polluting every object in the process.\n\n# Severity\nSuggested CVSS v3.1 `AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H` (8.1). The guaranteed impact is process-wide DoS / logic corruption; escalation to authorization bypass or RCE is dependent on gadgets in the consuming application.\n\n# Affected / Patched\n- Affected: `\u003c= 4.2.0` (verified in `3.0.0` and `4.2.0`; all 3.x and 4.x).\n- Patched: `4.3.0`.\n\n# Details\n`type` is a string *value*, untouched by `JSON.parse`, and is used directly as an object key:\n```js\nif (!models[type]) models[type] = {}          // models[\"__proto__\"] is Object.prototype \u2192 skipped\nif (!models[type][id]) models[type][id] = model // \u2192 Object.prototype[id] = model\n```\nThe attacker controls the polluted key (`id`) and value (the model, populated from `attributes`). Pollution persists for the process lifetime. The malicious type can also arrive via an `included` resource referenced by a relationship, bypassing any `data.type` allow-list. `LegacyStore` is additionally reachable when a configured `types` mapping resolves to `\"__proto__\"`.\n\n# Proof of concept\n```js\nconst { Store } = require(\u0027yayson\u0027)()\nnew Store().sync({ data: { type: \u0027__proto__\u0027, id: \u0027polluted\u0027, attributes: { x: 1 } } })\nconsole.log(({}).polluted) // { x: 1, id: \u0027polluted\u0027 }  \u2190 Object.prototype polluted\n```\n\n# Workarounds\nReject documents whose `type` or relationship names are `__proto__`, `constructor`, or `prototype`, or run Node with `--disable-proto=throw`.\n\n# Fix\nNull-prototype lookup tables, rejection of `__proto__`/`constructor`/`prototype` as document-derived member names, `Object.keys()` iteration, and null-prototype normalization of caller-supplied caches.",
  "id": "GHSA-325j-mg25-8q58",
  "modified": "2026-09-11T22:11:38Z",
  "published": "2026-09-11T22:11:38Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/confetti/yayson/security/advisories/GHSA-325j-mg25-8q58"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/confetti/yayson"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "yayson: Prototype pollution in Store/LegacyStore deserialization"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

CVE-2026-61534 (GCVE-0-2026-61534)

FKIE_CVE-2026-61534

GHSA-325J-MG25-8Q58

Summary

Severity

Affected / Patched

Details

Proof of concept

Workarounds

Fix

Tags

Sightings

Nomenclature