Prevent open redirect allow list bypass due to encodeurl

Co-authored-by: Jon Church <me@jonchurch.com>

lib/response.js

@@ -34,6 +34,7 @@ var extname = path.extname;
 var mime = send.mime;
 var resolve = path.resolve;
 var vary = require('vary');
+var urlParse = require('url').parse;
 
 /**
  * Response prototype.
@@ -911,8 +912,25 @@ res.location = function location(url) {
     loc = this.req.get('Referrer') || '/';
   }
 
+  var lowerLoc = loc.toLowerCase();
+  var encodedUrl = encodeUrl(loc);
+  if (lowerLoc.indexOf('https://') === 0 || lowerLoc.indexOf('http://') === 0) {
+    try {
+      var parsedUrl = urlParse(loc);
+      var parsedEncodedUrl = urlParse(encodedUrl);
+      // Because this can encode the host, check that we did not change the host
+      if (parsedUrl.host !== parsedEncodedUrl.host) {
+        // If the host changes after encodeUrl, return the original url
+        return this.set('Location', loc);
+      }
+    } catch (e) {
+      // If parse fails, return the original url
+      return this.set('Location', loc);
+    }
+  }
+
   // set location
-  return this.set('Location', encodeUrl(loc));
+  return this.set('Location', encodedUrl);
 };
 
 /**

test/res.location.js

@@ -1,13 +1,27 @@
 'use strict'
 
 var express = require('../')
-  , request = require('supertest');
+  , request = require('supertest')
+  , url = require('url');
 
 describe('res', function(){
   describe('.location(url)', function(){
     it('should set the header', function(done){
       var app = express();
 
+      app.use(function(req, res){
+        res.location('http://google.com/').end();
+      });
+
+      request(app)
+      .get('/')
+      .expect('Location', 'http://google.com/')
+      .expect(200, done)
+    })
+
+    it('should preserve trailing slashes when not present', function(done){
+      var app = express();
+
       app.use(function(req, res){
         res.location('http://google.com').end();
       });
@@ -31,6 +45,36 @@ describe('res', function(){
       .expect(200, done)
     })
 
+    it('should not encode bad "url"', function (done) {
+      var app = express()
+
+      app.use(function (req, res) {
+        // This is here to show a basic check one might do which
+        // would pass but then the location header would still be bad
+        if (url.parse(req.query.q).host !== 'google.com') {
+          res.status(400).end('Bad url');
+        }
+        res.location(req.query.q).end();
+      });
+
+      request(app)
+        .get('/?q=http://google.com\\@apple.com')
+        .expect(200)
+        .expect('Location', 'http://google.com\\@apple.com')
+        .end(function (err) {
+          if (err) {
+            throw err;
+          }
+
+          // This ensures that our protocol check is case insensitive
+          request(app)
+            .get('/?q=HTTP://google.com\\@apple.com')
+            .expect(200)
+            .expect('Location', 'HTTP://google.com\\@apple.com')
+            .end(done)
+        });
+    });
+
     it('should not touch already-encoded sequences in "url"', function (done) {
       var app = express()