The answer is a brute‑force attack. Event ID 4625 specifically logs failed logon attempts, and a sudden spike from random, external source IP addresses indicates an attacker systematically trying many password combinations across multiple accounts, which is the hallmark of a brute‑force attack. On the Computer Hacking Forensic Investigator CHFI exam, this scenario tests your ability to correlate Windows security logs with attack patterns, often appearing in questions about log analysis and intrusion detection. A common trap is confusing this with a dictionary attack, but remember that brute‑force attacks use random or sequential password attempts rather than a pre‑compiled wordlist. A useful memory tip: think of 4625 as “4-6-2-5” for “Four, Six, Two, Five” — “Four” failed attempts, “Six” random IPs, “Two” many accounts, “Five” brute‑force.
CHFI OS and Network Forensics Practice Question
This CHFI practice question tests your understanding of os and network forensics. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 detects a sudden spike in failed logon events with Event ID 4625 on a Windows domain controller. The source IP addresses are random and from various external subnets. 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 attack
Event ID 4625 indicates failed logon attempts. A sudden spike from random external IPs is characteristic of a brute‑force attack, where an attacker tries many passwords across multiple accounts.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Pass‑the‑hash attack
Why it's wrong here
Pass‑the‑hash would not necessarily generate many failed logon events; it uses stolen hashes to authenticate.
✗
Kerberos ticket forgery (Golden Ticket)
Why it's wrong here
Golden ticket attacks create forged Kerberos tickets, not multiple 4625 events.
✗
Insider threat with compromised credentials
Why it's wrong here
An insider would likely use a single IP, not random external ones.
✓
Brute‑force attack
Why this is correct
Correct. Many failed logons from varied IPs indicate a brute‑force attempt.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CHFI question in full detail.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CHFI subnetting questions on CIDR, address ranges, and subnet selection.
OS and Network Forensics — This question tests OS and Network Forensics — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Brute‑force attack — Event ID 4625 indicates failed logon attempts. A sudden spike from random external IPs is characteristic of a brute‑force attack, where an attacker tries many passwords across multiple accounts.
What should I do if I get this CHFI question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related CHFI subnetting questions on CIDR, address ranges, and subnet selection.
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?
CIDR notation defines the prefix length.
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