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Security Fundamentals & Crypto · Intermediate

Fail-Open

Failure mode where a system allows access or traffic to continue when it fails, favoring availability.

Definition

A fail-open device passes traffic or grants access on failure, preserving availability at the expense of security. Inline IPS sensors are often configured to fail open with hardware bypass so a sensor fault does not take down the network. The choice between fail-open and fail-closed is a risk decision.

Example

An inline IPS with a bypass module keeps forwarding traffic uninspected if the appliance crashes.

Exam tip

Fail-open favors availability; fail-closed (fail-secure) favors confidentiality and integrity.

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