Object serialization technologies allow programs to easily convert in-memory objects to and from various binary and textual data formats for storage or transfer – but with great power comes great responsibility, because deserializing objects from untrusted data can ruin your day. We will look at historical and modern vulnerabilities across different languages and serialization technologies, including Python, Ruby, and Java, and show how to exploit these issues to achieve code execution. We will also cover some strategies to protect applications from these types of attacks.