Ignore Object.prototype values in settings through app.set/app.get

closes #4802 closes #4803
expressjs · dougwilson · Apr 24, 2022 · Dec 5, 2021 · Dec 5, 2021 · May 20, 2021
commit c17fe058613dc7dfb7779fbe68a9738a108fe408
diff --git a/History.md b/History.md
@@ -1,6 +1,7 @@
 unreleased
 ==========
 
+  * Ignore `Object.prototype` values in settings through `app.set`/`app.get`
   * Support proper 205 responses using `res.send`
 
 4.17.3 / 2022-02-16

diff --git a/lib/application.js b/lib/application.js
@@ -29,6 +29,13 @@ var flatten = require('array-flatten');
 var merge = require('utils-merge');
 var resolve = require('path').resolve;
 var setPrototypeOf = require('setprototypeof')
+
+/**
+ * Module variables.
+ * @private
+ */
+
+var hasOwnProperty = Object.prototype.hasOwnProperty
 var slice = Array.prototype.slice;
 
 /**
@@ -352,7 +359,17 @@ app.param = function param(name, fn) {
 app.set = function set(setting, val) {
   if (arguments.length === 1) {
     // app.get(setting)
-    return this.settings[setting];
+    var settings = this.settings
+
+    while (settings && settings !== Object.prototype) {
+      if (hasOwnProperty.call(settings, setting)) {
+        return settings[setting]
+      }
+
+      settings = Object.getPrototypeOf(settings)
+    }
+
+    return undefined
   }
 
   debug('set "%s" to %o', setting, val);

diff --git a/test/config.js b/test/config.js
@@ -11,6 +11,12 @@ describe('config', function () {
       assert.equal(app.get('foo'), 'bar');
     })
 
+    it('should set prototype values', function () {
+      var app = express()
+      app.set('hasOwnProperty', 42)
+      assert.strictEqual(app.get('hasOwnProperty'), 42)
+    })
+
     it('should return the app', function () {
       var app = express();
       assert.equal(app.set('foo', 'bar'), app);
@@ -21,6 +27,17 @@ describe('config', function () {
       assert.equal(app.set('foo', undefined), app);
     })
 
+    it('should return set value', function () {
+      var app = express()
+      app.set('foo', 'bar')
+      assert.strictEqual(app.set('foo'), 'bar')
+    })
+
+    it('should return undefined for prototype values', function () {
+      var app = express()
+      assert.strictEqual(app.set('hasOwnProperty'), undefined)
+    })
+
     describe('"etag"', function(){
       it('should throw on bad value', function(){
         var app = express();
@@ -51,6 +68,11 @@ describe('config', function () {
       assert.strictEqual(app.get('foo'), undefined);
     })
 
+    it('should return undefined for prototype values', function () {
+      var app = express()
+      assert.strictEqual(app.get('hasOwnProperty'), undefined)
+    })
+
     it('should otherwise return the value', function(){
       var app = express();
       app.set('foo', 'bar');
@@ -125,6 +147,12 @@ describe('config', function () {
       assert.equal(app.enable('tobi'), app);
       assert.strictEqual(app.get('tobi'), true);
     })
+
+    it('should set prototype values', function () {
+      var app = express()
+      app.enable('hasOwnProperty')
+      assert.strictEqual(app.get('hasOwnProperty'), true)
+    })
   })
 
   describe('.disable()', function(){
@@ -133,6 +161,12 @@ describe('config', function () {
       assert.equal(app.disable('tobi'), app);
       assert.strictEqual(app.get('tobi'), false);
     })
+
+    it('should set prototype values', function () {
+      var app = express()
+      app.disable('hasOwnProperty')
+      assert.strictEqual(app.get('hasOwnProperty'), false)
+    })
   })
 
   describe('.enabled()', function(){
@@ -146,6 +180,11 @@ describe('config', function () {
       app.set('foo', 'bar');
       assert.strictEqual(app.enabled('foo'), true);
     })
+
+    it('should default to false for prototype values', function () {
+      var app = express()
+      assert.strictEqual(app.enabled('hasOwnProperty'), false)
+    })
   })
 
   describe('.disabled()', function(){
@@ -159,5 +198,10 @@ describe('config', function () {
       app.set('foo', 'bar');
       assert.strictEqual(app.disabled('foo'), false);
     })
+
+    it('should default to true for prototype values', function () {
+      var app = express()
+      assert.strictEqual(app.disabled('hasOwnProperty'), true)
+    })
   })
 })