easyMultiple Choice
ISC2 CC Practice Question: A security analyst notices repeated failed login…
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?
⚠ Common exam trap
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.
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
✓
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.
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 falsifies a source address so traffic appears to originate elsewhere; it does not generate repeated authentication failures against a VPN concentrator. It is tempting because spoofing underpins reflection and masquerade attacks, and would be the answer if the logs showed forged source IPs rather than brute-force attempts.
- ✓
Brute force
Why this is correct
Repeated failed authentications from one external IP against the VPN concentrator indicate systematic credential guessing, the defining pattern of brute force. The single source and high failure volume distinguish it from credential stuffing, which typically uses many distributed sources and leaked credential pairs.
- ✗
Man-in-the-Middle (MITM)
Why it's wrong here
MITM involves intercepting and relaying communications between two parties, which failed logins from one external IP do not demonstrate. It is tempting because VPNs carry sensitive traffic, but MITM is correct when an adversary sits between endpoints, not when authentication attempts are simply failing.
- ✗
Denial of Service (DoS)
Why it's wrong here
A DoS attack aims to exhaust resources and deny availability, not to guess credentials. It is tempting because repeated attempts resemble flooding, but DoS is correct when traffic saturates a service; here the pattern indicates credential guessing against authentication.
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
Go deeper
Related to this question
Key term
VPN
A VPN (Virtual Private Network) creates a secure, encrypted tunnel between your device and a remote server, protecting your data and hiding your online activity.
Key term
Vulnerability
A vulnerability is a weakness in a system, network, or software that could be exploited by a threat to cause harm or unauthorized access.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CC practice question is part of Courseiva's free ISC2 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 CC exam.