A boot-time check is a validation step performed by firmware before the operating system starts. It can inspect hardware identity, configuration, signatures, or other platform rules to decide whether the device is allowed to continue booting. Because it runs so early, it is more authoritative than normal software controls and can block the machine before drivers, security tools, or user recovery utilities are available.
In cyber security, boot-time checks are useful for enforcing trust, such as verifying approved components or stopping altered firmware and counterfeit hardware. They also create risk: if the logic is too strict, misconfigured, or based on weak identification, the result can be a denial of service that prevents a system from starting. Attackers may target this layer with bootkits, firmware tampering, or supply-chain manipulation, while defenders rely on secure boot, hardware attestation, and recovery paths to make early checks dependable.