A causal link is the provable connection between an act, a system behavior, and the harm that followed. In cyber security, it is the step that turns a suspicious event into a defensible conclusion: for example, whether a malicious login, a misconfiguration, or a poisoned input actually caused data loss, service failure, or an unsafe output. Logs, telemetry, timestamps, and configuration records are used to reconstruct that chain.
This matters because correlation is not proof. A crash after an alert does not by itself show the alert caused the crash. Defenders build causal links with incident timelines, packet captures, process trees, and change records; attackers often try to break them by deleting logs, using relays, or hiding inside normal system behavior. Strong traceability makes investigations, litigation, and remediation more reliable.