estree-util-value-to-estree allows prototype pollution in generated ESTree

Impact

When generating an ESTree from a value with a property named __proto__, valueToEstree would generate an object that specifies a prototype instead.

Example:

import { generate } from 'astring'
import { valueToEstree } from 'estree-util-value-to-estree'

const estree = valueToEstree({
  ['__proto__']: {}
})
const code = generate(estree)
console.log(code)

Output:

{
  "__proto__": {}
}

Patches

This was fixed in version 3.3.3.

Workarounds

If you control the input, don’t specify a property named __proto__. If you don’t control the output, strip any properties named __proto__ before passing it to valueToEstree.