fix(security): do not allow all origins by default

BREAKING CHANGE: previously, all origins were allowed by default, which
meant that a Socket.IO server sent the necessary CORS headers
(`Access-Control-Allow-xxx`) to any domain by default.

Please note that you are not impacted if:

- you are using Socket.IO v2 and the `origins` option to restrict the list of allowed domains
- you are using Socket.IO v3 (disabled by default)

This commit also removes the support for '*' matchers and protocol-less
URL:

```
io.origins('https://example.com:443'); => io.origins(['https://example.com']);
io.origins('localhost:3000');          => io.origins(['http://localhost:3000']);
io.origins('http://localhost:*');      => io.origins(['http://localhost:3000']);
io.origins('*:3000');                  => io.origins(['http://localhost:3000']);
```

To restore the previous behavior (please use with caution):

```js
io.origins((_, callback) => {
  callback(null, true);
});
```

See also:

- https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS
- https://socket.io/docs/v3/handling-cors/
- https://socket.io/docs/v3/migrating-from-2-x-to-3-0/#CORS-handling

Thanks a lot to https://github.com/ni8walk3r for the security report.

lib/index.js

@@ -54,7 +54,7 @@ function Server(srv, opts){
   this.parser = opts.parser || parser;
   this.encoder = new this.parser.Encoder();
   this.adapter(opts.adapter || Adapter);
-  this.origins(opts.origins || '*:*');
+  this.origins(opts.origins || []);
   this.sockets = this.of('/');
   if (srv) this.attach(srv, opts);
 }
@@ -67,31 +67,18 @@ function Server(srv, opts){
  */
 
 Server.prototype.checkRequest = function(req, fn) {
-  var origin = req.headers.origin || req.headers.referer;
+  const origin = req.headers.origin;
 
-  // file:// URLs produce a null Origin which can't be authorized via echo-back
-  if ('null' == origin || null == origin) origin = '*';
+  if (typeof this._origins === 'function') {
+    return this._origins(origin, fn);
+  }
 
-  if (!!origin && typeof(this._origins) == 'function') return this._origins(origin, fn);
-  if (this._origins.indexOf('*:*') !== -1) return fn(null, true);
   if (origin) {
-    try {
-      var parts = url.parse(origin);
-      var defaultPort = 'https:' == parts.protocol ? 443 : 80;
-      parts.port = parts.port != null
-        ? parts.port
-        : defaultPort;
-      var ok =
-        ~this._origins.indexOf(parts.protocol + '//' + parts.hostname + ':' + parts.port) ||
-        ~this._origins.indexOf(parts.hostname + ':' + parts.port) ||
-        ~this._origins.indexOf(parts.hostname + ':*') ||
-        ~this._origins.indexOf('*:' + parts.port);
-      debug('origin %s is %svalid', origin, !!ok ? '' : 'not ');
-      return fn(null, !!ok);
-    } catch (ex) {
-    }
+    fn(null, this._origins.includes(origin));
+  } else {
+    const noOriginIsValid = this._origins.length === 0;
+    fn(null, noOriginIsValid);
   }
-  fn(null, false);
 };
 
 /**
@@ -237,7 +224,7 @@ Server.prototype.adapter = function(v){
 Server.prototype.origins = function(v){
   if (!arguments.length) return this._origins;
 
-  this._origins = v;
+  this._origins = typeof v === 'string' ? [v] : v;
   return this;
 };
 

test/socket.io.js

@@ -73,7 +73,7 @@ describe('socket.io', function(){
     it('should be able to set origins to engine.io', function() {
       var srv = io(http());
       srv.set('origins', 'http://hostname.com:*');
-      expect(srv.origins()).to.be('http://hostname.com:*');
+      expect(srv.origins()).to.eql(['http://hostname.com:*']);
     });
 
     it('should be able to set authorization and send error packet', function(done) {
@@ -262,17 +262,6 @@ describe('socket.io', function(){
        });
     });
 
-    it('should allow request when origin defined an the same is specified', function(done) {
-      var sockets = io({ origins: 'http://foo.example:*' }).listen('54015');
-      request.get('http://localhost:54015/socket.io/default/')
-       .set('origin', 'http://foo.example')
-       .query({ transport: 'polling' })
-       .end(function (err, res) {
-          expect(res.status).to.be(200);
-          done();
-        });
-    });
-
     it('should allow request when origin defined as function and same is supplied', function(done) {
       var sockets = io({ origins: function(origin,callback){
         if (origin == 'http://foo.example') {
@@ -307,7 +296,7 @@ describe('socket.io', function(){
 
     it('should allow request when origin defined as function and no origin is supplied', function(done) {
       var sockets = io({ origins: function(origin,callback){
-        if (origin == '*') {
+        if (origin === undefined) {
           return callback(null, true);
         }
         return callback(null, false);
@@ -320,17 +309,6 @@ describe('socket.io', function(){
         });
     });
 
-    it('should default to port 443 when protocol is https', function(done) {
-      var sockets = io({ origins: 'https://foo.example:443' }).listen('54036');
-      request.get('http://localhost:54036/socket.io/default/')
-        .set('origin', 'https://foo.example')
-        .query({ transport: 'polling' })
-        .end(function (err, res) {
-          expect(res.status).to.be(200);
-          done();
-        });
-    });
-
     it('should allow request if custom function in opts.allowRequest returns true', function(done){
       var sockets = io(http().listen(54022), { allowRequest: function (req, callback) {
         return callback(null, true);
@@ -367,6 +345,17 @@ describe('socket.io', function(){
           done();
         });
     });
+
+    it('should disallow any origin by default', (done) => {
+      io().listen('54025');
+      request.get('http://localhost:54025/socket.io/default/')
+        .set('origin', 'https://foo.example')
+        .query({ transport: 'polling' })
+        .end((err, res) => {
+          expect(res.status).to.be(403);
+          done();
+        });
+    });
   });
 
   describe('close', function(){