Fix. Code. Protects against PTR spoofing

Author: AntonV1211

inc/cleantalk-public-integrations.php

@@ -164,9 +164,10 @@ function ct_woocommerce_wishlist_check($args)
         }
     }
 
-    //If the IP is a Google bot
-    $hostname = gethostbyaddr(TT::toString(Server::get('REMOTE_ADDR')));
-    if ( ! strpos($hostname, 'googlebot.com') ) {
+    //If the IP is a Google bot (with FCrDNS verification to prevent PTR spoofing)
+    $client_ip = TT::toString(Server::get('REMOTE_ADDR'));
+    $verified_hostname = \Cleantalk\Common\Helper::ipResolve($client_ip);
+    if ( ! $verified_hostname || strpos($verified_hostname, 'googlebot.com') === false ) {
         do_action('apbct_skipped_request', __FILE__ . ' -> ' . __FUNCTION__ . '():' . __LINE__, $_POST);
 
         return $args;

lib/Cleantalk/Antispam/Cleantalk.php

@@ -479,7 +479,8 @@ public function httpPing($host)
             $file = @fsockopen($host, 443, $errno, $errstr, $this->max_server_timeout / 1000);
         } else {
             $http = new Request();
-            $host = 'https://' . gethostbyaddr($host);
+            $verified_host = Helper::ipResolve($host);
+            $host = 'https://' . ($verified_host ?: $host);
             $file = $http->setUrl($host)
                 ->setOptions(['timeout' => $this->max_server_timeout / 1000])
                 ->setPresets('get_code get')

lib/Cleantalk/ApbctWP/RemoteCalls.php

@@ -56,11 +56,14 @@ public static function checkWithoutToken()
             'netserv3.cleantalk.org',
             'netserv4.cleantalk.org',
         ];
-
+        // Resolve IP of the client making the request and verify hostname from it to be in the list of RC servers hostnames
+        $client_ip = Helper::ipGet('remote_addr');
+        $verified_hostname = $client_ip ? \Cleantalk\Common\Helper::ipResolve($client_ip) : false;
         $is_noc_request = ! $apbct->key_is_ok &&
             Request::get('spbc_remote_call_action') &&
             in_array(Request::get('plugin_name'), array('antispam', 'anti-spam', 'apbct')) &&
-            in_array(Helper::ipResolve(Helper::ipGet('remote_addr')), $rc_servers, true);
+            $verified_hostname !== false &&
+            in_array($verified_hostname, $rc_servers, true);
 
         // no token needs for this action, at least for now
         // todo Probably we still need to validate this, consult with analytics team

lib/Cleantalk/Common/DNS.php

@@ -114,7 +114,9 @@ public static function getResponseTime($host)
             $file = @fsockopen($host, 443, $errno, $errstr, static::$max_server_timeout / 1000);
         } else {
             $http = new Request();
-            $host = 'https://' . gethostbyaddr($host);
+            // Use FCrDNS-verified hostname, or IP directly if verification fails
+            $verified_host = Helper::ipResolve($host);
+            $host = 'https://' . ($verified_host ?: $host);
             $file = $http->setUrl($host)
                 ->setOptions(['timeout' => static::$max_server_timeout / 1000])
                 ->setPresets('get_code get')

lib/Cleantalk/Common/Helper.php

@@ -528,22 +528,43 @@ public static function ipV6Reduce($ip)
     }
 
     /**
-     * Get URL form IP
+     * Resolve IP to hostname with FCrDNS (Forward-Confirmed reverse DNS) verification.
+     * Protects against PTR spoofing by verifying the hostname resolves back to the same IP.
      *
-     * @param $ip
+     * @param string $ip IP address to resolve
      *
-     * @return string
+     * @return string|false Verified hostname or false on failure
      */
     public static function ipResolve($ip)
     {
-        if (self::ipValidate($ip)) {
-            $url = gethostbyaddr($ip);
-            if ($url) {
-                return $url;
-            }
+        // Validate IP first
+        if (!self::ipValidate($ip)) {
+            return false;
         }
 
-        return $ip;
+        // Reverse DNS lookup (PTR record)
+        $hostname = gethostbyaddr($ip);
+
+        // If gethostbyaddr returns the IP itself, it means no PTR record exists
+        if (!$hostname || $hostname === $ip) {
+            return false;
+        }
+
+        // Forward DNS lookup (A/AAAA records) - verify the hostname points back to the IP
+        $forward_ips = gethostbynamel($hostname);
+
+        // If forward lookup fails, we can't verify
+        if (!$forward_ips) {
+            return false;
+        }
+
+        // Check if the original IP is in the list of IPs the hostname resolves to
+        if (in_array($ip, $forward_ips, true)) {
+            return $hostname;
+        }
+
+        // FCrDNS verification failed - possible PTR spoofing attempt
+        return false;
     }
 
     /**