A deserialization attack occurs when a cybercriminal exploits the process by which a computer program converts data from a stored format back into usable objects. If a system accepts serialized data from untrusted sources and does not properly validate it, attackers can send specially crafted data that, when deserialized, executes harmful code or alters program behavior. This can lead to severe consequences such as unauthorized access, data breaches, or even full system compromise. These attacks are particularly dangerous in applications that use serialization for data exchange, as they often assume incoming data is safe.