Use Object.create(null) to avoid default object property hazards

ini.js

@@ -18,7 +18,7 @@ function encode (obj, opt) {
       whitespace: false
     }
   } else {
-    opt = opt || {}
+    opt = opt || Object.create(null)
     opt.whitespace = opt.whitespace === true
   }
 
@@ -67,7 +67,7 @@ function dotSplit (str) {
 }
 
 function decode (str) {
-  var out = {}
+  var out = Object.create(null)
   var p = out
   var section = null
   //          section     |key      = value
@@ -83,13 +83,14 @@ function decode (str) {
       if (section === '__proto__') {
         // not allowed
         // keep parsing the section, but don't attach it.
-        p = {}
+        p = Object.create(null)
         return
       }
-      p = out[section] = out[section] || {}
+      p = out[section] = out[section] || Object.create(null)
       return
     }
     var key = unsafe(match[2])
+    if (key === '__proto__') return
     var value = match[3] ? unsafe(match[4]) : true
     switch (value) {
       case 'true':
@@ -133,7 +134,7 @@ function decode (str) {
     var nl = l.replace(/\\\./g, '.')
     parts.forEach(function (part, _, __) {
       if (part === '__proto__') return
-      if (!p[part] || typeof p[part] !== 'object') p[part] = {}
+      if (!p[part] || typeof p[part] !== 'object') p[part] = Object.create(null)
       p = p[part]
     })
     if (p === out && nl === l) {

test/proto.js

@@ -3,6 +3,7 @@ var t = require('tap')
 
 var data = `
 __proto__ = quux
+constructor.prototype.foo = asdfasdf
 foo = baz
 [__proto__]
 foo = bar
@@ -15,27 +16,39 @@ hello = snyk
 __proto__[] = you did a good job
 __proto__[] = so you deserve arrays
 thanks = true
+[ctor.constructor.prototype]
+foo = asdfasdf
 `
+
 var res = ini.parse(data)
-t.deepEqual(res, {
+
+t.deepEqual(res, Object.assign(Object.create(null), {
+  'constructor.prototype.foo': 'asdfasdf',
   foo: 'baz',
-  other: {
+  other: Object.assign(Object.create(null), {
     foo: 'asdf',
-  },
-  kid: {
-    foo: {
+  }),
+  kid: Object.assign(Object.create(null), {
+    foo: Object.assign(Object.create(null), {
       foo: 'kid',
-    },
-  },
-  arrproto: {
+    }),
+  }),
+  arrproto: Object.assign(Object.create(null), {
     hello: 'snyk',
     thanks: true,
-  },
-})
-t.equal(res.__proto__, Object.prototype)
-t.equal(res.kid.__proto__, Object.prototype)
-t.equal(res.kid.foo.__proto__, Object.prototype)
-t.equal(res.arrproto.__proto__, Object.prototype)
+  }),
+  ctor: Object.assign(Object.create(null), {
+    constructor: Object.assign(Object.create(null), {
+      prototype: Object.assign(Object.create(null), {
+        foo: 'asdfasdf',
+      }),
+    }),
+  }),
+}))
+t.equal(res.__proto__, undefined)
+t.equal(res.kid.__proto__, undefined)
+t.equal(res.kid.foo.__proto__, undefined)
+t.equal(res.arrproto.__proto__, undefined)
 t.equal(Object.prototype.foo, undefined)
 t.equal(Object.prototype[0], undefined)
 t.equal(Object.prototype['0'], undefined)