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Interview question · Systems, OS & Memory Safety

Design privilege separation for a network-facing service, and explain how to drop privileges so they cannot be regained.

OpenSSH's design is the model answer, but interviewers want you to derive it: what the parser must never hold, how small the privileged half can get, and the three mistakes that make a privilege drop reversible.

hardNewPreparation tags: Google, Microsoft, AppleUpdated Nov 2026

OpenSSH's design is the model answer, but interviewers want you to derive it: what the parser must never hold, how small the privileged half can get, and the three mistakes that make a privilege drop reversible.

Make your first attempt

What would you say before reading the answer?

  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

The worked answer includes an approach, scoring criteria and follow-up questions. Compare the reasoning with your own.

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What if · the follow-ups in this answer

The answer works through 6 follow-ups like an interviewer would

A network daemon parses untrusted input and also needs to read a private key for authentication.

  1. What is privilege separation?
  2. How does OpenSSH apply it?
  3. What makes the broker interface safe?
  4. How do you confine the unprivileged side?
  5. What does this cost?
  6. How would you design the daemon?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Sign in free to open it.

UP NEXT ON YOUR JOURNEY
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