A package lifecycle hook is code that a package manager runs automatically at a specific event, such as install, postinstall, preuninstall, or upgrade. In practice, it behaves like a built-in trigger: when a package is added or updated, the hook can execute commands without the user launching them directly.
This matters in cyber security because lifecycle hooks turn software installation into a code-execution moment. Attackers can hide malicious behavior in a poisoned package, letting the hook run on a developer workstation or build runner and then steal tokens, service-account credentials, or other secrets. Defenders watch for unexpected install-time scripts, restrict execution during package installs, verify package provenance, and use least-privilege systems so a single package cannot reach sensitive cloud or CI/CD identities.