This CS0-003 practice question tests your understanding of incident response and management. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
During incident response, the team identifies that an attacker used a compromised third-party vendor account to access the network. Which of the following should the team do first?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "first"
Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Change all system passwords
Why wrong: Password reset is a broader action; revoking the specific account is more immediate.
Revoke the vendor's access
Stops the attacker from using the compromised account.
Conduct forensic analysis on the vendor's account
Why wrong: Forensic analysis should follow containment to preserve evidence.
Notify law enforcement
Why wrong: Law enforcement notification is important but not the first priority.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Revoke the vendor's access
The immediate priority is to contain the breach by revoking the compromised third-party vendor's access. This stops the attacker from using the valid session or credentials to move laterally or exfiltrate data. Changing all system passwords (A) is too broad and time-consuming, while forensic analysis (C) and law enforcement notification (D) are secondary steps that occur after containment.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Change all system passwords
Why it's wrong here
Password reset is a broader action; revoking the specific account is more immediate.
Revoke the vendor's access
Why this is correct
Stops the attacker from using the compromised account.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Conduct forensic analysis on the vendor's account
Why it's wrong here
Forensic analysis should follow containment to preserve evidence.
Notify law enforcement
Why it's wrong here
Law enforcement notification is important but not the first priority.
Common exam traps
CompTIA often tests the 'containment before eradication' principle, and the trap here is that candidates choose forensic analysis (C) first, mistakenly thinking evidence preservation is more urgent than stopping the active attack.
Detailed technical explanation
In incident response frameworks like NIST SP 800-61, containment is the first priority after identification. Revoking the vendor's access may involve disabling the account in the identity provider (IdP), invalidating OAuth tokens, or terminating active VPN sessions. A real-world scenario is the 2020 SolarWinds breach, where delayed revocation of compromised vendor accounts allowed attackers to persist for months.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A SOC analyst notices unusual lateral movement in the network at 2 AM. The IR playbook dictates: identify and contain (isolate the affected machine), then eradicate (remove the malware), then recover (restore from backup), then document. Skipping containment before eradication risks the attacker regaining access. Questions like this test the sequence and rationale of incident response phases.
What to study next
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FAQ
Incident Response and Management — This question tests Incident Response and Management — Read the scenario before looking for a memorised answer..
The correct answer is: Revoke the vendor's access — The immediate priority is to contain the breach by revoking the compromised third-party vendor's access. This stops the attacker from using the valid session or credentials to move laterally or exfiltrate data. Changing all system passwords (A) is too broad and time-consuming, while forensic analysis (C) and law enforcement notification (D) are secondary steps that occur after containment.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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