tls: fix object prototype type confusion

Use `Object.create(null)` for dictionary objects so that keys from
certificate strings or the authorityInfoAccess field cannot conflict
with Object.prototype properties.

Author: bnoordhuis

lib/_tls_common.js

@@ -176,14 +176,11 @@ exports.translatePeerCertificate = function translatePeerCertificate(c) {
   if (c.subject != null) c.subject = tls.parseCertString(c.subject);
   if (c.infoAccess != null) {
     var info = c.infoAccess;
-    c.infoAccess = {};
+    c.infoAccess = Object.create(null);
 
     // XXX: More key validation?
     info.replace(/([^\n:]*):([^\n]*)(?:\n|$)/g, function(all, key, val) {
-      if (key === '__proto__')
-        return;
-
-      if (c.infoAccess.hasOwnProperty(key))
+      if (key in c.infoAccess)
         c.infoAccess[key].push(val);
       else
         c.infoAccess[key] = [val];

lib/tls.js

@@ -231,7 +231,7 @@ exports.checkServerIdentity = function checkServerIdentity(host, cert) {
 // Example:
 // C=US\nST=CA\nL=SF\nO=Joyent\nOU=Node.js\nCN=ca1\nemailAddress=ry@clouds.org
 exports.parseCertString = function parseCertString(s) {
-  var out = {};
+  var out = Object.create(null);
   var parts = s.split('\n');
   for (var i = 0, len = parts.length; i < len; i++) {
     var sepIndex = parts[i].indexOf('=');

test/parallel/test-tls-parse-cert-string.js

@@ -1,3 +1,4 @@
+/* eslint-disable no-proto */
 'use strict';
 const common = require('../common');
 if (!common.hasCrypto)
@@ -11,6 +12,7 @@ const tls = require('tls');
                   'CN=ca1\nemailAddress=ry@clouds.org';
   const singlesOut = tls.parseCertString(singles);
   assert.deepStrictEqual(singlesOut, {
+    __proto__: null,
     C: 'US',
     ST: 'CA',
     L: 'SF',
@@ -26,6 +28,7 @@ const tls = require('tls');
                   'CN=*.nodejs.org';
   const doublesOut = tls.parseCertString(doubles);
   assert.deepStrictEqual(doublesOut, {
+    __proto__: null,
     OU: [ 'Domain Control Validated', 'PositiveSSL Wildcard' ],
     CN: '*.nodejs.org'
   });
@@ -34,5 +37,13 @@ const tls = require('tls');
 {
   const invalid = 'fhqwhgads';
   const invalidOut = tls.parseCertString(invalid);
-  assert.deepStrictEqual(invalidOut, {});
+  assert.deepStrictEqual(invalidOut, { __proto__: null });
+}
+
+{
+  const input = '__proto__=mostly harmless\nhasOwnProperty=not a function';
+  const expected = Object.create(null);
+  expected.__proto__ = 'mostly harmless';
+  expected.hasOwnProperty = 'not a function';
+  assert.deepStrictEqual(tls.parseCertString(input), expected);
 }

test/parallel/test-tls-translate-peer-certificate.js

@@ -1,3 +1,4 @@
+/* eslint-disable no-proto */
 'use strict';
 const common = require('../common');
 
@@ -7,8 +8,12 @@ if (!common.hasCrypto)
 const { strictEqual, deepStrictEqual } = require('assert');
 const { translatePeerCertificate } = require('_tls_common');
 
-const certString = 'A=1\nB=2\nC=3';
-const certObject = { A: '1', B: '2', C: '3' };
+const certString = '__proto__=42\nA=1\nB=2\nC=3';
+const certObject = Object.create(null);
+certObject.__proto__ = '42';
+certObject.A = '1';
+certObject.B = '2';
+certObject.C = '3';
 
 strictEqual(translatePeerCertificate(null), null);
 strictEqual(translatePeerCertificate(undefined), null);
@@ -19,14 +24,14 @@ strictEqual(translatePeerCertificate(1), 1);
 deepStrictEqual(translatePeerCertificate({}), {});
 
 deepStrictEqual(translatePeerCertificate({ issuer: '' }),
-                { issuer: {} });
+                { issuer: Object.create(null) });
 deepStrictEqual(translatePeerCertificate({ issuer: null }),
                 { issuer: null });
 deepStrictEqual(translatePeerCertificate({ issuer: certString }),
                 { issuer: certObject });
 
 deepStrictEqual(translatePeerCertificate({ subject: '' }),
-                { subject: {} });
+                { subject: Object.create(null) });
 deepStrictEqual(translatePeerCertificate({ subject: null }),
                 { subject: null });
 deepStrictEqual(translatePeerCertificate({ subject: certString }),
@@ -47,9 +52,18 @@ deepStrictEqual(
 }
 
 deepStrictEqual(translatePeerCertificate({ infoAccess: '' }),
-                { infoAccess: {} });
+                { infoAccess: Object.create(null) });
 deepStrictEqual(translatePeerCertificate({ infoAccess: null }),
                 { infoAccess: null });
-deepStrictEqual(
-  translatePeerCertificate({ infoAccess: 'OCSP - URI:file:///etc/passwd' }),
-  { infoAccess: { 'OCSP - URI': ['file:///etc/passwd'] } });
+{
+  const input =
+      '__proto__:mostly harmless\n' +
+      'hasOwnProperty:not a function\n' +
+      'OCSP - URI:file:///etc/passwd\n';
+  const expected = Object.create(null);
+  expected.__proto__ = ['mostly harmless'];
+  expected.hasOwnProperty = ['not a function'];
+  expected['OCSP - URI'] = ['file:///etc/passwd'];
+  deepStrictEqual(translatePeerCertificate({ infoAccess: input }),
+                  { infoAccess: expected });
+}