The correct answer is a brute force attack. This is because the security analyst observed repeated failed login attempts from a single external IP address targeting the VPN concentrator, which is the classic signature of an attacker systematically trying numerous username and password combinations until they find a valid one. The attack exploits weak or common credentials rather than a protocol vulnerability, making it distinct from a dictionary attack (which uses a precompiled list) or a password spraying attack (which tries one password across many accounts). On the ISC2 Certified in Cybersecurity CC exam, this scenario tests your ability to differentiate between brute force, dictionary, and spraying attacks—a common trap is confusing brute force with password spraying, but remember that brute force focuses many attempts on a single target account or entry point. Memory tip: think of a battering ram hitting the same door repeatedly—that’s brute force.
ISC2 CC Network Security Practice Question
This CC practice question tests your understanding of network security. 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 security analyst notices repeated failed login attempts from a single external IP address targeting the company's VPN concentrator. Which type of attack is most likely occurring?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Brute force
Repeated failed login attempts from a single external IP targeting a VPN concentrator are the hallmark of a brute force attack. The attacker systematically tries many username/password combinations to gain unauthorized access, exploiting weak or common credentials rather than exploiting a protocol vulnerability.
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.
✗
Spoofing
Why it's wrong here
Spoofing involves falsifying IP addresses; this symptom does not indicate spoofing.
✓
Brute force
Why this is correct
Brute force attacks involve repeated guessing of credentials, matching this behavior.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Man-in-the-Middle (MITM)
Why it's wrong here
MITM attacks intercept communications; they do not typically produce repeated login failures from a single IP.
✗
Denial of Service (DoS)
Why it's wrong here
DoS attacks aim to overwhelm the system with traffic, not specifically login attempts.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the distinction between a brute force attack (focused on credential guessing) and a Denial of Service attack (focused on resource exhaustion), where candidates mistakenly choose DoS because repeated attempts seem to 'overwhelm' the system, but the core intent is unauthorized access, not service disruption.
Detailed technical explanation
How to think about this question
VPN concentrators often implement rate limiting or account lockout policies to mitigate brute force attacks, but attackers can bypass these by rotating through multiple usernames with a single password (password spraying) or using distributed IPs. Under the hood, the VPN concentrator's authentication logs (e.g., syslog or RADIUS accounting) will show multiple 'Authentication failure' events from the same source IP, which is a key indicator for security teams. In real-world scenarios, attackers use tools like Hydra or Medusa to automate these attempts, targeting common VPN protocols like IPsec IKE or SSL/TLS-based VPNs.
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
A security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CC question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Brute force — Repeated failed login attempts from a single external IP targeting a VPN concentrator are the hallmark of a brute force attack. The attacker systematically tries many username/password combinations to gain unauthorized access, exploiting weak or common credentials rather than exploiting a protocol vulnerability.
What should I do if I get this CC 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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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