Enforce configured CORS origins

.github/workflows/ci.yml

@@ -128,7 +128,7 @@ jobs:
         run: docker compose -f compose.yml -f compose.dev.yml up -d mongo redis
 
       - name: Start server
-        run: LETSCUBE_TEST_AUTH=true SOCIAL_FEATURES_ENABLED=true POSTGRES_ENABLED=false yarn workspace letscube-server node index.js > server.log 2>&1 &
+        run: CORS_ORIGINS=http://localhost:3000,http://localhost:8080 LETSCUBE_TEST_AUTH=true SOCIAL_FEATURES_ENABLED=true POSTGRES_ENABLED=false yarn workspace letscube-server node index.js > server.log 2>&1 &
 
       - name: Start socket server
         run: SOCIAL_FEATURES_ENABLED=true POSTGRES_ENABLED=false yarn workspace letscube-server node socket/ > socket.log 2>&1 &

server/index.js

@@ -11,6 +11,7 @@ const { connect } = require('./database');
 const { createHealthHandler, createHealthReporter } = require('./health');
 const { initializePostgres, pool, startPostgresMaintenance } = require('./postgres');
 const session = require('./middlewares/session');
+const { createCorsOptions } = require('./middlewares/cors');
 const logger = require('./logger');
 const auth = require('./auth');
 const api = require('./api');
@@ -73,11 +74,7 @@ const init = async () => {
 
   /* Cors */
 
-  app.use(cors({
-    credentials: true,
-    origin: true,
-    // config.cors.origin.map((o) => new RegExp(o)),
-  }));
+  app.use(cors(createCorsOptions(config.cors.origin)));
 
   app.get('/api/csrf-token', (req, res) => res.json({ csrfToken: req.csrfToken() }));
 

server/middlewares/cors.js

@@ -0,0 +1,10 @@
+const createCorsOptions = (origins) => {
+  const allowedOrigins = new Set(origins);
+
+  return {
+    credentials: true,
+    origin: (origin, callback) => callback(null, !origin || allowedOrigins.has(origin)),
+  };
+};
+
+module.exports = { createCorsOptions };

server/middlewares/cors.test.js

@@ -0,0 +1,62 @@
+/** @jest-environment node */
+/* eslint-env jest */
+
+const http = require('http');
+const cors = require('cors');
+const express = require('express');
+const { createCorsOptions } = require('./cors');
+
+const request = (server, origin) => new Promise((resolve, reject) => {
+  const req = http.request({
+    headers: origin ? { origin } : {},
+    host: '127.0.0.1',
+    method: 'GET',
+    path: '/',
+    port: server.address().port,
+  }, (res) => {
+    res.resume();
+    res.on('end', () => resolve({ headers: res.headers, status: res.statusCode }));
+  });
+  req.on('error', reject);
+  req.end();
+});
+
+describe('CORS origin allowlist', () => {
+  let server;
+
+  beforeEach((done) => {
+    const app = express();
+    app.use(cors(createCorsOptions(['https://letscube.net', 'http://localhost:3000'])));
+    app.get('/', (req, res) => res.json({ ok: true }));
+    server = app.listen(0, '127.0.0.1', () => done());
+  });
+
+  afterEach((done) => {
+    server.close(() => done());
+  });
+
+  it('permits configured credentialed browser origins', async () => {
+    const response = await request(server, 'https://letscube.net');
+
+    expect(response).toEqual(expect.objectContaining({ status: 200 }));
+    expect(response.headers).toEqual(expect.objectContaining({
+      'access-control-allow-credentials': 'true',
+      'access-control-allow-origin': 'https://letscube.net',
+    }));
+  });
+
+  it('does not grant CORS permission to an unconfigured origin', async () => {
+    const response = await request(server, 'https://untrusted.example');
+
+    expect(response).toEqual(expect.objectContaining({ status: 200 }));
+    expect(response.headers).not.toHaveProperty('access-control-allow-credentials');
+    expect(response.headers).not.toHaveProperty('access-control-allow-origin');
+  });
+
+  it('leaves same-origin and non-browser requests working', async () => {
+    const response = await request(server);
+
+    expect(response).toEqual(expect.objectContaining({ status: 200 }));
+    expect(response.headers).not.toHaveProperty('access-control-allow-origin');
+  });
+});