lib: add warning when binding inspector to public IP

Add `isLoopback` function to `internal/net` module to check if a given
host is a loopback address.

Add a warning when binding the inspector to a public IP with an open
port, as it allows external hosts to connect to the inspector.

Fixes: nodejs#23444
Refs: https://nodejs.org/api/cli.html#--inspecthostport

lib/inspector.js

@@ -18,6 +18,8 @@ const {
   ERR_INSPECTOR_NOT_WORKER,
 } = require('internal/errors').codes;
 
+const { isLoopback } = require('internal/net');
+
 const { hasInspector } = internalBinding('config');
 if (!hasInspector)
   throw new ERR_INSPECTOR_NOT_AVAILABLE();
@@ -171,6 +173,16 @@ function inspectorOpen(port, host, wait) {
   if (isUint32(port)) {
     validateInt32(port, 'port', 0, 65535);
   }
+  if (host && !isLoopback(host)) {
+    process.emitWarning(
+      'Binding the inspector to a public IP with an open port is insecure, ',
+      'as it allows external hosts to connect to the inspector ',
+      'and perform a remote code execution attack.',
+      'Documentation can be found at ' +
+        'https://nodejs.org/api/cli.html#--inspecthostport',
+    );
+  }
+
   open(port, host);
   if (wait)
     waitForDebugger();

lib/internal/net.js

@@ -68,11 +68,23 @@ function makeSyncWrite(fd) {
   };
 }
 
+function isLoopback(host) {
+  const hostLower = host.toLowerCase();
+
+  return (
+    hostLower === 'localhost' ||
+    hostLower.startsWith('127.') ||
+    hostLower.startsWith('[::1]') ||
+    hostLower.startsWith('[0:0:0:0:0:0:0:1]')
+  );
+}
+
 module.exports = {
   kReinitializeHandle: Symbol('kReinitializeHandle'),
   isIP,
   isIPv4,
   isIPv6,
   makeSyncWrite,
   normalizedArgsSymbol: Symbol('normalizedArgs'),
+  isLoopback,
 };

test/parallel/test-internal-net-isLoopback.js

@@ -0,0 +1,32 @@
+// Flags: --expose-internals
+'use strict';
+require('../common');
+const assert = require('assert');
+const net = require('internal/net');
+
+const loopback = [
+  'localhost',
+  '127.0.0.1',
+  '127.0.0.255',
+  '127.1.2.3',
+  '[::1]',
+  '[0:0:0:0:0:0:0:1]',
+];
+
+const loopbackNot = [
+  'example.com',
+  '192.168.1.1',
+  '10.0.0.1',
+  '255.255.255.255',
+  '[2001:db8::1]',
+  '[fe80::1]',
+  '8.8.8.8',
+];
+
+for (const address of loopback) {
+  assert.strictEqual(net.isLoopback(address), true);
+}
+
+for (const address of loopbackNot) {
+  assert.strictEqual(net.isLoopback(address), false);
+}