Insecure deserialization is a vulnerability that occurs when untrusted or user-supplied data is deserialized by an application without proper validation. This flaw allows attackers to manipulate serialized objects, potentially leading to remote code execution, privilege escalation, or other malicious activities. Attackers can exploit insecure deserialization to inject arbitrary objects or data, bypass authentication, or tamper with application logic. Common targets include web applications that use serialization mechanisms for session management or data storage. Preventing insecure deserialization involves validating and sanitizing input, using safe serialization formats, and implementing integrity checks to ensure that only trusted data is processed.