GitHub Advisoryadvisory · npm
GHSA-vj54-72f3-p5jv devalue prototype pollution vulnerability
HIGH
Official page ↗
- Aliases
- CVE-2025-57820
- Ecosystem
- npm
- Packages
- devalue
- Severity
- High
- CVSS vector
- 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
- Weaknesses
- CWE-1321
- Reviewed
- 2025-08-26
Affected packages
• npm devalue: < 5.3.2 → fixed in 5.3.2
Description
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:
```js
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:
```js
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:
```js
const object = devalue.parse('[{"toString":"push"}]');
object.toString(); // 0
```
This could be used by a creative attacker to bypass server-side validation.
Related
Alias · CVE (1)
- CVE-2025-57820 Svelte devalue is a utility library. vulnerability
Weakness · CWE (1)
- CWE-1321 Improperly Controlled Modification of Object Prototype Attributes weakness