secure-json-parse

secure-json-parse

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

Introduction

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.

Install

npm i secure-json-parse

Usage

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' }))

API

sjson.parse(text, [reviver], [options])

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).
  • safe - optional boolean:
    • true - returns null instead of throwing when a forbidden prototype property is found.
    • false - default behavior (throws or removes based on protoAction/constructorAction).

sjson.scan(obj, [options])

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.
  • safe - optional boolean:
    • true - returns null instead of throwing when a forbidden prototype property is found.
    • false - default behavior (throws or removes based on protoAction/constructorAction).

Benchmarks

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

Acknowledgments

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.

License

Licensed under BSD-3-Clause.

Similar packages

Other packages similar to secure-json-parse

fast-json-parse

fast-json-parse is a package that focuses on providing a fast and safe way to parse JSON strings. While it emphasizes performance, it may not offer the same level of security features specifically designed to prevent prototype pollution attacks as secure-json-parse does.

flatted

flatted is a package that offers JSON parsing and stringifying with support for circular references. While it addresses a different aspect of JSON handling (circular references), it does not specifically focus on security concerns like prototype pollution, which is the main focus of secure-json-parse.