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Interview question · Systems, OS & Memory Safety

How does NTLM authentication work, how do relay and coercion attacks abuse it, and which signing and binding controls stop them?

NTLM proves you can answer a challenge. It never proves which server you meant to answer, so whoever sits in the middle can pass your answer to a server you never chose.

hardEssentialNewPreparation tags: Microsoft, CrowdStrike, Palo Alto NetworksUpdated Nov 2026

NTLM proves you can answer a challenge. It never proves which server you meant to answer, so whoever sits in the middle can pass your answer to a server you never chose.

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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.

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What if · the follow-ups in this answer

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

An attacker on the internal network can make a server authenticate to them, and NTLM is still enabled in the domain.

  1. How does NTLM authentication work?
  2. Why can it be relayed?
  3. Why is coerced server authentication dangerous?
  4. Which defences block relay?
  5. How would you reduce NTLM use?
  6. How would you protect the domain?

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