A GDPR lawful basis is the legal reason that makes processing personal data permitted under EU privacy law. Common bases include consent, contract, legal obligation, vital interests, public task, and legitimate interests. Organizations must choose the correct basis before collecting or using personal data, and they must be able to justify that choice with records and policy.
This matters in cyber security because security tools often process personal data: logs, alerts, device identifiers, IP addresses, and user activity records. Defenders need a lawful basis to monitor systems, investigate incidents, retain evidence, and share data with third parties. Attackers may try to exploit weak privacy governance, for example by abusing excessive access or poorly controlled telemetry. Good security practice therefore links technical controls with privacy accountability, ensuring the data collected for defense is necessary, proportionate, and processed under a valid legal ground.