JSON.parse() drop-in replacement with prototype poisoning protection.

Consider this:

> const a = '{"__proto__":{ "b":5}}'; '{"__proto__":{ "b":5}}' > const b = JSON.parse(a); { __proto__: { b: 5 } } > b.b; undefined > const c = Object.assign({}, b); {} > c.b 5

The problem is that JSON.parse() retains the __proto__ property as a plain object key. By itself, this is not a security issue. However, as soon as that object is assigned to another or iterated on and values copied, the __proto__ property leaks and becomes the object's prototype.

npm i secure-json-parse 

Pass the option object as a second (or third) parameter for configuring the action to take in case of a bad JSON, if nothing is configured, the default is to throw a SyntaxError.
You can choose which action to perform in case __proto__ is present, and in case constructor.prototype is present.

const sjson = require('secure-json-parse') const goodJson = '{ "a": 5, "b": 6 }' const badJson = '{ "a": 5, "b": 6, "__proto__": { "x": 7 }, "constructor": {"prototype": {"bar": "baz"} } }' console.log(JSON.parse(goodJson), sjson.parse(goodJson, undefined, { protoAction: 'remove', constructorAction: 'remove' })) console.log(JSON.parse(badJson), sjson.parse(badJson, undefined, { protoAction: 'remove', constructorAction: 'remove' }))

Parses a given JSON-formatted text into an object where:

• text - the JSON text string.
• reviver - the JSON.parse() optional reviver argument.
• options - optional configuration object where:
  • protoAction - optional string with one of:
    • 'error' - throw a SyntaxError when a __proto__ key is found. This is the default value.
    • 'remove' - deletes any __proto__ keys from the result object.
    • 'ignore' - skips all validation (same as calling JSON.parse() directly).
  • constructorAction - optional string with one of:
    • 'error' - throw a SyntaxError when a constructor.prototype key is found. This is the default value.
    • 'remove' - deletes any constructor keys from the result object.
    • 'ignore' - skips all validation (same as calling JSON.parse() directly).

Scans a given object for prototype properties where:

• obj - the object being scanned.
• options - optional configuration object where:
  • protoAction - optional string with one of:
    • 'error' - throw a SyntaxError when a __proto__ key is found. This is the default value.
    • 'remove' - deletes any __proto__ keys from the input obj.
  • constructorAction - optional string with one of:
    • 'error' - throw a SyntaxError when a constructor.prototype key is found. This is the default value.
    • 'remove' - deletes any constructor keys from the input obj.

Machine: 2,7 GHz Quad-Core Intel Core i7

v14.8.0 > node ignore.js JSON.parse x 679,376 ops/sec ±1.15% (84 runs sampled) secure-json-parse x 649,605 ops/sec ±0.58% (87 runs sampled) reviver x 244,414 ops/sec ±1.05% (88 runs sampled) Fastest is JSON.parse > node no__proto__.js JSON.parse x 652,190 ops/sec ±0.67% (86 runs sampled) secure-json-parse x 589,785 ops/sec ±1.01% (88 runs sampled) reviver x 218,075 ops/sec ±1.58% (87 runs sampled) Fastest is JSON.parse > node remove.js JSON.parse x 683,527 ops/sec ±0.62% (88 runs sampled) secure-json-parse x 316,926 ops/sec ±0.63% (87 runs sampled) reviver x 214,167 ops/sec ±0.63% (86 runs sampled) Fastest is JSON.parse > node throw.js JSON.parse x 682,548 ops/sec ±0.60% (88 runs sampled) JSON.parse error x 170,716 ops/sec ±0.93% (87 runs sampled) secure-json-parse x 104,483 ops/sec ±0.62% (87 runs sampled) reviver x 114,197 ops/sec ±0.63% (87 runs sampled) Fastest is JSON.parse 

This project has been forked from hapijs/bourne. All credit before commit 4690682 goes to the hapijs/bourne project contributors. After, the project will be maintained by the Fastify team.

Licensed under BSD-3-Clause.