- A
Replay attack, because a captured valid authentication message was resent to gain access again.
Replay attacks work by capturing a legitimate authentication message and submitting it later, often before it expires or is invalidated.
- B
ARP poisoning, because the attacker redirected traffic by altering local address resolution.
Why wrong: ARP poisoning changes link-layer mapping on a local network, but it does not explain repeated acceptance of the same authentication blob.
- C
Phishing, because the user was tricked into entering credentials on a fake page.
Why wrong: Phishing is a social engineering technique that targets user input, whereas this scenario centers on reuse of captured protocol data.
- D
Denial of service, because the attacker is overwhelming the VPN gateway with requests.
Why wrong: The issue is unauthorized access through reuse of a valid message, not service exhaustion or outage.
Quick Answer
The answer is a replay attack, because a captured authentication blob was retransmitted to gain unauthorized access. This attack works by intercepting a valid authentication message—such as a VPN pre-shared key hash or a Kerberos ticket—and resending it to the server, which mistakenly treats the duplicate as a fresh, legitimate request. On the Security+ SY0-701 exam, this scenario tests your understanding of authentication integrity and the need for protections like timestamps, sequence numbers, or nonces to prevent reuse. A common trap is confusing this with a man-in-the-middle or pass-the-hash attack, but the key distinction here is the simple re-sending of an unchanged blob without any interception or modification of the session. Memory tip: think “replay” as in “re-play” a recorded message—if the server accepts the same token twice, it’s a replay.
SY0-701 Threats, Vulnerabilities, and Mitigations Practice Question
This SY0-701 practice question tests your understanding of threats, vulnerabilities, and mitigations. 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.
A VPN concentrator shows that an authentication request from a user was accepted twice, even though the user insists they approved only one login. Packet analysis reveals that the second successful attempt reused the same authentication blob and arrived shortly after the first. Which attack is the best fit?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Replay attack, because a captured valid authentication message was resent to gain access again.
The scenario describes a captured authentication blob being reused to gain a second successful authentication. This is the hallmark of a replay attack, where an attacker intercepts a valid authentication message (e.g., a Kerberos TGT, RADIUS Access-Accept, or a VPN pre-shared key hash) and retransmits it to the VPN concentrator to impersonate the user. The VPN concentrator accepted the duplicate because it lacked proper replay protection mechanisms such as timestamps, sequence numbers, or one-time-use nonces.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Replay attack, because a captured valid authentication message was resent to gain access again.
Why this is correct
Replay attacks work by capturing a legitimate authentication message and submitting it later, often before it expires or is invalidated.
Clue confirmation
The clue words "best", "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
ARP poisoning, because the attacker redirected traffic by altering local address resolution.
Why it's wrong here
ARP poisoning changes link-layer mapping on a local network, but it does not explain repeated acceptance of the same authentication blob.
- ✗
Phishing, because the user was tricked into entering credentials on a fake page.
Why it's wrong here
Phishing is a social engineering technique that targets user input, whereas this scenario centers on reuse of captured protocol data.
- ✗
Denial of service, because the attacker is overwhelming the VPN gateway with requests.
Why it's wrong here
The issue is unauthorized access through reuse of a valid message, not service exhaustion or outage.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is confusing a replay attack with a phishing attack, because both involve capturing authentication data, but replay attacks reuse the captured blob directly without tricking the user, while phishing requires the user to voluntarily submit credentials.
Trap categories for this question
Scenario analysis trap
Phishing is a social engineering technique that targets user input, whereas this scenario centers on reuse of captured protocol data.
Detailed technical explanation
How to think about this question
Replay attacks exploit the lack of freshness in authentication protocols. In VPN contexts, protocols like IKEv2 or L2TP/IPsec often use nonces and sequence numbers to prevent replay; if these are missing or improperly implemented, an attacker can capture a valid authentication blob (e.g., an IKE_AUTH response) and replay it within the validity window. Real-world examples include replaying a RADIUS Access-Accept packet to gain VPN access without valid credentials, which was a known issue in older implementations without Message-Authenticator attributes.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An employee at a financial services firm receives an email that appears to come from the IT helpdesk, asking them to reset their password via a link. The link leads to a convincing fake portal that harvests credentials. Security teams use phishing simulations and security-awareness training to reduce this attack vector. Questions like this test whether you can identify social engineering techniques and appropriate controls.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this SY0-701 question test?
Threats, Vulnerabilities, and Mitigations — This question tests Threats, Vulnerabilities, and Mitigations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Replay attack, because a captured valid authentication message was resent to gain access again. — The scenario describes a captured authentication blob being reused to gain a second successful authentication. This is the hallmark of a replay attack, where an attacker intercepts a valid authentication message (e.g., a Kerberos TGT, RADIUS Access-Accept, or a VPN pre-shared key hash) and retransmits it to the VPN concentrator to impersonate the user. The VPN concentrator accepted the duplicate because it lacked proper replay protection mechanisms such as timestamps, sequence numbers, or one-time-use nonces.
What should I do if I get this SY0-701 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "best", "first". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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Last reviewed: Jun 11, 2026
This SY0-701 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SY0-701 exam.
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