4 OPC UA security architecture

4.3 Security threats to OPC UA systems

4.3.6 Message replay

Network traffic and valid application layer Messages may be captured and resent to OPC UA Clients, Servers and Subscribers at a later stage without modification. An attacker could misinform the user or send a valid command such as opening a valve but at an improper time, so as to cause damage or property loss. An attacker may attempt to establish a Session using a recorded Session.

Message replay impacts Authorization and during Session / secure channel establishment Authentication. See 5.1.6 for the reconciliation of this threat.