For Client-Server, an attacker can send a large volume of Messages, or a single Messagethat contains a large number of requests, with the goal of overwhelming the OPC UA Serveror dependent components such as CPU, TCP/IP stack, operating system, or the file system. Flooding attacks can be conducted at multiple layers including OPC UA, SOAP, [HTTP] or TCP.

Messageflooding attacks can use both well-formed and malformed Messages. In the first scenario, the attacker could be a malicious person using a legitimate Clientto flood the Serverwith requests. Two cases exist, one in which the Clientdoes not have a Session with the Serverand one in which it does. Messageflooding may impair the ability to establish OPC UA Sessionsor terminate an existing Session. In the second scenario, an attacker could use a malicious Clientthat floods an OPC UA Serverwith malformed Messages in order to exhaust the Server’s resources.

For PubSub, an attacker can send a large volume of dataset messages with the goal of overwhelming the subscriber, the middleware or dependent components such as CPU, TCP/IP stack, operating system, or the file system. Flooding attacks can be conducted at multiple layers including OPC UA, UDP, AMQP, MQTT.

As in Client-Server, PubSubmessage flooding attacks can use both well-formed and malformed Messages. For well-formed Messages, the attacker could be one in which the publisher is not a member of the SecurityGroupand one in which it is a member. For malformed Messages, an attacker could use a malicious Publisherthat floods a network with malformed Messagesin order to exhaust the system’s resources.

In general, Messageflooding may impair the ability to communicate with an OPC UA entity and result in denial of service.