Description

devalue prototype pollution vulnerability

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;...
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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.

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