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Security Operations · Foundational

Backdoor

A hidden method of bypassing normal authentication or security controls to access a system.

Definition

Backdoors may be installed by malware, left by developers for maintenance, or inserted through supply chain compromise. They provide persistent access even after the original vulnerability is fixed. Examples include hidden accounts, web shells, and implants listening on unusual ports.

Example

An attacker creating a hidden local administrator account to regain access after passwords are reset.

Exam tip

After an incident, eradication must remove all backdoors or attackers will return.

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