fix: allow CORS from loopback addresses by default

docs/config/server-options.md

@@ -161,7 +161,7 @@ export default defineConfig({
 ## server.cors
 
 - **Type:** `boolean | CorsOptions`
-- **Default:** `false`
+- **Default:** `{ origin: /^https?:\/\/(?:(?:[^:]+\.)?localhost|127\.0\.0\.1|\[::1\])(?::\d+)?$/ }` (allows localhost, `127.0.0.1` and `::1`)
 
 Configure CORS for the dev server. Pass an [options object](https://github.com/expressjs/cors#configuration-options) to fine tune the behavior or `true` to allow any origin.
 

packages/vite/src/node/__tests__/constants.spec.ts

@@ -0,0 +1,32 @@
+import { expect, test } from 'vitest'
+import { defaultAllowedOrigins } from '../constants'
+
+test('defaultAllowedOrigins', () => {
+  const allowed = [
+    'http://localhost',
+    'http://foo.localhost',
+    'http://localhost:3000',
+    'https://localhost:3000',
+    'http://127.0.0.1',
+    'http://[::1]',
+    'http://[::1]:3000',
+  ]
+  const denied = [
+    'file:///foo',
+    'http://localhost.example.com',
+    'http://foo.example.com:localhost',
+    'http://',
+    'http://192.0.2',
+    'http://[2001:db8::1]',
+    'http://vite',
+    'http://vite:3000',
+  ]
+
+  for (const origin of allowed) {
+    expect(defaultAllowedOrigins.test(origin), origin).toBe(true)
+  }
+
+  for (const origin of denied) {
+    expect(defaultAllowedOrigins.test(origin), origin).toBe(false)
+  }
+})

packages/vite/src/node/constants.ts

@@ -183,6 +183,13 @@ export const DEFAULT_PREVIEW_PORT = 4173
 
 export const DEFAULT_ASSETS_INLINE_LIMIT = 4096
 
+// the regex to allow loopback address origins:
+// - localhost domains (which will always resolve to the loopback address by RFC 6761 section 6.3)
+// - 127.0.0.1
+// - ::1
+export const defaultAllowedOrigins =
+  /^https?:\/\/(?:(?:[^:]+\.)?localhost|127\.0\.0\.1|\[::1\])(?::\d+)?$/
+
 export const METADATA_FILENAME = '_metadata.json'
 
 export const ERR_OPTIMIZE_DEPS_PROCESSING_ERROR =

packages/vite/src/node/server/index.ts

@@ -44,7 +44,11 @@ import { reloadOnTsconfigChange } from '../plugins/esbuild'
 import { bindCLIShortcuts } from '../shortcuts'
 import type { BindCLIShortcutsOptions } from '../shortcuts'
 import { ERR_OUTDATED_OPTIMIZED_DEP } from '../../shared/constants'
-import { CLIENT_DIR, DEFAULT_DEV_PORT } from '../constants'
+import {
+  CLIENT_DIR,
+  DEFAULT_DEV_PORT,
+  defaultAllowedOrigins,
+} from '../constants'
 import type { Logger } from '../logger'
 import { printServerUrls } from '../logger'
 import { warnFutureDeprecation } from '../deprecations'
@@ -1055,7 +1059,7 @@ export const serverConfigDefaults = Object.freeze({
   https: undefined,
   open: false,
   proxy: undefined,
-  cors: false,
+  cors: { origin: defaultAllowedOrigins },
   headers: {},
   // hmr
   // ws