fix: restrict CORS to localhost origins only

Prevents cross-origin attacks from malicious websites by restricting
CORS to only allow:
- Requests without Origin header (hooks, curl, CLI tools)
- Requests from localhost / 127.0.0.1 origins

Previously, CORS was completely open (cors() without configuration),
allowing any website to access the local API and read session data.

src/services/worker/http/middleware.ts

@@ -24,8 +24,21 @@ export function createMiddleware(
   // JSON parsing with 50mb limit
   middlewares.push(express.json({ limit: '50mb' }));
 
-  // CORS
-  middlewares.push(cors());
+  // CORS - restrict to localhost origins only
+  middlewares.push(cors({
+    origin: (origin, callback) => {
+      // Allow: requests without Origin header (hooks, curl, CLI tools)
+      // Allow: localhost and 127.0.0.1 origins
+      if (!origin ||
+          origin.startsWith('http://localhost:') ||
+          origin.startsWith('http://127.0.0.1:')) {
+        callback(null, true);
+      } else {
+        callback(new Error('CORS not allowed'));
+      }
+    },
+    credentials: false
+  }));
 
   // HTTP request/response logging
   middlewares.push((req: Request, res: Response, next: NextFunction) => {

tests/worker/middleware/cors-restriction.test.ts

@@ -0,0 +1,62 @@
+/**
+ * CORS Restriction Tests
+ *
+ * Verifies that CORS is properly restricted to localhost origins only.
+ * This prevents cross-origin attacks from malicious websites.
+ */
+
+import { describe, it, expect } from 'bun:test';
+
+// Test the CORS origin validation logic directly
+function isAllowedOrigin(origin: string | undefined): boolean {
+  if (!origin) return true; // No origin = hooks, curl, CLI
+  if (origin.startsWith('http://localhost:')) return true;
+  if (origin.startsWith('http://127.0.0.1:')) return true;
+  return false;
+}
+
+describe('CORS Restriction', () => {
+  describe('allowed origins', () => {
+    it('allows requests without Origin header (hooks, curl, CLI)', () => {
+      expect(isAllowedOrigin(undefined)).toBe(true);
+    });
+
+    it('allows localhost with port', () => {
+      expect(isAllowedOrigin('http://localhost:37777')).toBe(true);
+      expect(isAllowedOrigin('http://localhost:3000')).toBe(true);
+      expect(isAllowedOrigin('http://localhost:8080')).toBe(true);
+    });
+
+    it('allows 127.0.0.1 with port', () => {
+      expect(isAllowedOrigin('http://127.0.0.1:37777')).toBe(true);
+      expect(isAllowedOrigin('http://127.0.0.1:3000')).toBe(true);
+    });
+  });
+
+  describe('blocked origins', () => {
+    it('blocks external domains', () => {
+      expect(isAllowedOrigin('http://evil.com')).toBe(false);
+      expect(isAllowedOrigin('https://attacker.io')).toBe(false);
+      expect(isAllowedOrigin('http://malicious-site.net:8080')).toBe(false);
+    });
+
+    it('blocks HTTPS localhost (not typically used for local dev)', () => {
+      // HTTPS localhost is unusual and could indicate a proxy attack
+      expect(isAllowedOrigin('https://localhost:37777')).toBe(false);
+    });
+
+    it('blocks localhost-like domains (subdomain attacks)', () => {
+      expect(isAllowedOrigin('http://localhost.evil.com')).toBe(false);
+      expect(isAllowedOrigin('http://localhost.attacker.io:8080')).toBe(false);
+    });
+
+    it('blocks file:// origins', () => {
+      expect(isAllowedOrigin('file://')).toBe(false);
+    });
+
+    it('blocks null origin', () => {
+      // null origin can come from sandboxed iframes
+      expect(isAllowedOrigin('null')).toBe(false);
+    });
+  });
+});