An output plugin is a dynamically loaded module used by PostgreSQL logical decoding to format change data and send it to a consumer. Logical decoding extracts row-level changes from the write-ahead log, and the output plugin decides how those changes are represented, such as text, JSON, or a custom binary format. Because the plugin is loaded as executable code, it is part of the database’s attack surface, not just a data-formatting detail.
This matters in cyber security because any feature that loads a module at runtime can cross a privilege boundary. If an attacker can influence which plugin is selected, or can place a malicious library where the server will load it, a replication workflow may become a code execution path instead of a data stream. Defenders should treat approved plugins like software dependencies: restrict who can use replication features, limit library search paths, remove unneeded plugins, and keep PostgreSQL patched. In short, an output plugin is the trusted formatter between database changes and the outside world, so trust and loading rules must be tightly controlled.