The answer is that an attacker successfully brute-forced the root password. This conclusion is drawn directly from the forensic evidence in the auth.log file, where a sequence of multiple 'Failed password for root' entries from a single IP address is immediately followed by an 'Accepted password for root' entry from the same IP, indicating the attacker systematically guessed passwords until one worked. On the Computer Hacking Forensic Investigator CHFI exam, this scenario tests your ability to interpret Linux authentication logs and distinguish between a successful brute-force attack and a mere scanning attempt; a common trap is to assume that any failed logins are just reconnaissance, but the presence of a subsequent successful login from the same source IP confirms the attack succeeded. A useful memory tip for this pattern is "fail then accept from one IP equals cracked," which helps you quickly spot the signature of a completed brute-force attack in auth.log.
CHFI OS and Network Forensics Practice Question
This CHFI practice question tests your understanding of os and network forensics. 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 a Linux forensic investigation, you find that the /var/log/auth.log file contains log entries showing multiple 'Failed password for root' messages from a single IP address, followed by a 'Accepted password for root' entry. What is the MOST likely conclusion?
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
✓
An attacker successfully brute-forced the root password
The pattern suggests a successful brute-force attack: multiple failed attempts and then a successful authentication from the same IP.
Key principle: Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
An attacker successfully brute-forced the root password
Why this is correct
Failed followed by accepted from same IP indicates successful brute force.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
The root user accidentally mistyped the password multiple times
Why it's wrong here
While possible, the pattern is more indicative of an automated brute-force attack.
✗
The system was compromised via a privilege escalation exploit
Why it's wrong here
No evidence of privilege escalation; SSH logon was used.
✗
The root account has been locked out due to multiple failures
Why it's wrong here
There is an accepted entry, so account was not locked.
Common exam traps
Common exam trap: authentication is not authorization
Logging in proves the user can authenticate. It does not automatically mean the user is allowed to enter privileged or configuration mode. Watch for AAA authorization, privilege level and command authorization details.
Detailed technical explanation
How to think about this question
This kind of question is testing the difference between identity and permission. A user may successfully log in to a router because authentication is working, but still fail to enter configuration mode because authorization is missing, misconfigured or mapped to a lower privilege level.
KKey Concepts to Remember
Authentication checks who the user is.
Authorization controls what the user is allowed to do after login.
Privilege levels affect access to EXEC and configuration commands.
AAA, TACACS+ and RADIUS can separate login success from command access.
TExam Day Tips
→Do not assume successful login means full administrative access.
→Look for words such as cannot enter configuration mode, privilege level, authorization or command access.
→Separate login problems from permission problems before choosing the answer.
Key takeaway
Authentication proves identity; authorization controls what that identity can do after login. Both must work for full privileged access.
Real-world example
How this comes up in practice
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CHFI question in full detail.
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related CHFI questions on access control and AAA configuration.
OS and Network Forensics — This question tests OS and Network Forensics — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: An attacker successfully brute-forced the root password — The pattern suggests a successful brute-force attack: multiple failed attempts and then a successful authentication from the same IP.
What should I do if I get this CHFI question wrong?
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related CHFI questions on access control and AAA configuration.
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?
Authentication checks who the user is.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. In Linux forensics, an investigator examines /var/log/auth.log and finds repeated entries of "Failed password for root from 10.0.0.5 port 22 ssh2". Which type of attack is most likely indicated?
easy
A.DNS cache poisoning attack
B.SQL injection attack
C.ARP spoofing attack
✓ D.Brute force attack on SSH
Why D: Repeated failed SSH login attempts for the root user from a single IP address is a classic sign of a brute force attack against SSH.
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This CHFI practice question is part of Courseiva's free EC-Council 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 CHFI exam.
Question Discussion
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