feat: Protect against prototype poisoning

follow fastify/fastify#1427

throw SyntaxError when prototype poisoning happen by default

Readme.md

@@ -24,6 +24,10 @@ $ npm install co-body
 
   - `limit` number or string representing the request size limit (1mb for json and 56kb for form-urlencoded)
   - `strict` when set to `true`, JSON parser will only accept arrays and objects; when `false` will accept anything `JSON.parse` accepts. Defaults to `true`. (also `strict` mode will always return object).
+  - `onProtoPoisoning` Defines what action the `co-body` lib must take when parsing a JSON object with `__proto__`. This functionality is provided by [bourne](https://github.com/hapijs/bourne).
+    See [Prototype-Poisoning](https://fastify.dev/docs/latest/Guides/Prototype-Poisoning/) for more details about prototype poisoning attacks.
+    Possible values are `'error'`, `'remove'` and `'ignore'`.
+    Default to `'error'`, it will throw a `SyntaxError` when `Prototype-Poisoning` happen.
   - `queryString` an object of options when parsing query strings and form data. See [qs](https://github.com/hapijs/qs) for more information.
   - `returnRawBody` when set to `true`, the return value of `co-body` will be an object with two properties: `{ parsed: /* parsed value */, raw: /* raw body */}`.
   - `jsonTypes` is used to determine what media type **co-body** will parse as **json**, this option is passed directly to the [type-is](https://github.com/jshttp/type-is) library.

lib/json.js

@@ -6,6 +6,7 @@
 
 const raw = require('raw-body');
 const inflate = require('inflation');
+const bourne = require('@hapi/bourne');
 const utils = require('./utils');
 
 // Allowed whitespace is defined in RFC 7159
@@ -35,6 +36,7 @@ module.exports = async function(req, opts) {
   opts.encoding = opts.encoding || 'utf8';
   opts.limit = opts.limit || '1mb';
   const strict = opts.strict !== false;
+  const protoAction = opts.onProtoPoisoning || 'error';
 
   const str = await raw(inflate(req), opts);
   try {
@@ -47,13 +49,13 @@ module.exports = async function(req, opts) {
   }
 
   function parse(str) {
-    if (!strict) return str ? JSON.parse(str) : str;
+    if (!strict) return str ? bourne.parse(str, { protoAction }) : str;
     // strict mode always return object
     if (!str) return {};
     // strict JSON test
     if (!strictJSONReg.test(str)) {
       throw new SyntaxError('invalid JSON, only supports object and array');
     }
-    return JSON.parse(str);
+    return bourne.parse(str, { protoAction });
   }
 };

package.json

@@ -13,6 +13,7 @@
     "urlencoded"
   ],
   "dependencies": {
+    "@hapi/bourne": "^3.0.0",
     "inflation": "^2.0.0",
     "qs": "^6.5.2",
     "raw-body": "^2.3.3",

test/json.test.js

@@ -158,4 +158,58 @@ describe('parse.json(req, opts)', function() {
         .expect(200, done);
     });
   });
+
+  describe('with valid onProtoPoisoning', function() {
+    it('should parse with onProtoPoisoning = "error" by default', function(done) {
+      const app = koa();
+
+      app.use(function* () {
+        try {
+          yield parse.json(this);
+        } catch (err) {
+          err.should.be.an.instanceOf(SyntaxError);
+          err.message.should.equal('Object contains forbidden prototype property');
+          err.status.should.equal(400);
+          err.body.should.equal('{ "__proto__": { "boom": "💣" } }');
+          done();
+        }
+      });
+
+      request(app.callback())
+        .post('/')
+        .set('content-type', 'application/json')
+        .send('{ "__proto__": { "boom": "💣" } }')
+        .end(function() {});
+    });
+
+    it('should parse with onProtoPoisoning = "ignore"', function(done) {
+      const app = koa();
+
+      app.use(function* () {
+        this.body = yield parse.json(this, { onProtoPoisoning: 'ignore' });
+      });
+
+      request(app.callback())
+        .post('/')
+        .set('content-type', 'application/json')
+        .send('{ "__proto__": { "boom": "💣" }, "hello": "world" }')
+        .expect({ ['__proto__']: { boom: '💣' }, hello: 'world' })
+        .expect(200, done);
+    });
+
+    it('should parse with onProtoPoisoning = "remove"', function(done) {
+      const app = koa();
+
+      app.use(function* () {
+        this.body = yield parse.json(this, { onProtoPoisoning: 'remove' });
+      });
+
+      request(app.callback())
+        .post('/')
+        .set('content-type', 'application/json')
+        .send('{ "__proto__": { "boom": "💣" }, "hello": "world" }')
+        .expect({ hello: 'world' })
+        .expect(200, done);
+    });
+  });
 });