Resolve hostnames from whitelist

default/config.yaml

@@ -42,6 +42,7 @@ enableForwardedWhitelist: true
 whitelist:
   - ::1
   - 127.0.0.1
+  - host.docker.internal
 # Toggle basic authentication for endpoints
 basicAuthMode: false
 # Basic authentication credentials

src/middleware/whitelist.js

@@ -1,7 +1,9 @@
 import path from 'node:path';
 import fs from 'node:fs';
 import process from 'node:process';
+import dns from 'node:dns';
 import Handlebars from 'handlebars';
+import ipRegex from 'ip-regex';
 import ipMatching from 'ip-matching';
 
 import { getIpFromRequest } from '../express-common.js';
@@ -20,6 +22,8 @@ if (fs.existsSync(whitelistPath)) {
     }
 }
 
+await resolveHostnames();
+
 /**
  * Get the client IP address from the request headers.
  * @param {import('express').Request} req Express request object
@@ -45,6 +49,65 @@ function getForwardedIp(req) {
     return undefined;
 }
 
+/**
+ * Checks if a string is a valid hostname according to RFC 1123
+ * @param {string} hostname The string to test
+ * @returns {boolean} True if the string is a valid hostname
+ */
+function isValidHostname(hostname) {
+    const hostnameRegex = /^(([a-z0-9]|[a-z0-9][a-z0-9-]*[a-z0-9])\.)*([a-z0-9]|[a-z0-9][a-z0-9-]*[a-z0-9])$/i;
+    return hostnameRegex.test(hostname);
+}
+
+/**
+ * Checks if a string is an IP address, CIDR notation, or IP wildcard
+ * @param {string} entry The string to test
+ * @returns {boolean} True if the string matches any IP format
+ */
+function isIpFormat(entry) {
+    // Match CIDR notation (e.g. 192.168.0.0/24)
+    if (entry.includes('/')) {
+        return true;
+    }
+
+    // Match exact IP address
+    if (ipRegex({ exact: true }).test(entry)) {
+        return true;
+    }
+
+    // Match IPv4 with wildcards (e.g. 192.168.*.* or 192.168.0.*)
+    const ipWildcardRegex = /^(\d{1,3}|\*)\.(\d{1,3}|\*)\.(\d{1,3}|\*)\.(\d{1,3}|\*)$/;
+    return ipWildcardRegex.test(entry);
+}
+
+/**
+ * Validate the IP addresses in the whitelist.
+ * Hostnames are resolved to IP addresses.
+ */
+async function resolveHostnames() {
+    for (let i = 0; i < whitelist.length; i++) {
+        try {
+            const entry = whitelist[i];
+
+            // Skip if entry appears to be an IP address, CIDR notation, or IP wildcard
+            if (isIpFormat(entry)) {
+                continue;
+            }
+
+            if (isValidHostname(entry)) {
+                const result = await dns.promises.lookup(entry);
+
+                if (result.address) {
+                    console.info('Resolved whitelist hostname', entry, 'to IP address', result.address);
+                    whitelist[i] = result.address;
+                }
+            }
+        } catch {
+            // Ignore errors when resolving hostnames
+        }
+    }
+}
+
 /**
  * Returns a middleware function that checks if the client IP is in the whitelist.
  * @returns {import('express').RequestHandler} The middleware function