A gadget chain is a sequence of existing classes, methods, and callbacks that an attacker can combine to produce harmful behavior during deserialization. Each individual piece may look safe on its own, but together they create an execution path the developer never intended. In practice, the chain is built from code already present in the application or its libraries, so exploitation often depends on what gems, packages, or framework components are loaded.
Gadget chains matter because they turn trusted runtime features into attack surfaces. When untrusted data reaches deserialization sinks such as Ruby’s Marshal.load, the runtime may rebuild objects and invoke hooks like marshal_load automatically. That can lead to unexpected method calls, data corruption, or remote code execution if a usable chain exists. Defenders reduce this risk by avoiding deserialization of attacker-controlled data, preferring simple formats for external input, and minimizing exposed callbacks and unnecessary libraries.