fix: always allow localhost to connect to dev server

lib/Server.js

@@ -3121,6 +3121,10 @@ class Server {
     }
 
     // always allow localhost host, for convenience
+    if (value === "localhost" || value.endsWith(".localhost")) {
+      return true;
+    }
+
     // allow if value is in allowedHosts
     if (Array.isArray(allowedHosts) && allowedHosts.length > 0) {
       for (let hostIdx = 0; hostIdx < allowedHosts.length; hostIdx++) {
@@ -3210,14 +3214,10 @@ class Server {
     // an IPv6-address in URLs,
     // these are removed from the hostname in url.parse(),
     // so we have the pure IPv6-address in hostname.
-    // For convenience, always allow localhost (hostname === 'localhost')
-    // and its subdomains (hostname.endsWith(".localhost")).
     // allow hostname of listening address  (hostname === this.options.host)
     const isValidHostname =
       ipaddr.IPv4.isValid(hostname) ||
       ipaddr.IPv6.isValid(hostname) ||
-      hostname === "localhost" ||
-      hostname.endsWith(".localhost") ||
       hostname === this.options.host;
 
     if (isValidHostname) {

test/server/same-origin.test.js

@@ -0,0 +1,41 @@
+"use strict";
+
+const webpack = require("webpack");
+const Server = require("../../lib/Server");
+const config = require("../fixtures/simple-config/webpack.config");
+
+describe("isSameOrigin", () => {
+  let server;
+
+  beforeEach(async () => {
+    const compiler = webpack(config);
+    server = new Server({}, compiler);
+  });
+
+  it("should return true for localhost", () => {
+    const headers = {
+      host: "localhost:8080",
+      origin: "http://localhost:8080",
+    };
+
+    expect(server.isSameOrigin(headers)).toBe(true);
+  });
+
+  it("should return true for localhost subdomains", () => {
+    const headers = {
+      host: "localhost:8080",
+      origin: "http://subdomain.localhost:8080",
+    };
+
+    expect(server.isSameOrigin(headers)).toBe(true);
+  });
+
+  it("should return false for cross-origin requests", () => {
+    const headers = {
+      origin: "http://example.com",
+      host: "attacker.com",
+    };
+
+    expect(server.isSameOrigin(headers)).toBe(false);
+  });
+});