The most likely cause is that the remote user's system clock is not synchronized with the domain controller. Kerberos authentication is extremely sensitive to time skew, with a default maximum tolerance of just five minutes as defined in RFC 4120; when users connect via VPN, their local clocks often drift from the domain’s authoritative time source, causing the authentication service to reject ticket requests and produce an ‘Access Denied’ error even though the VPN tunnel itself is up and RADIUS authentication succeeds. On the Systems Security Certified Practitioner SSCP exam, this scenario tests your understanding of Kerberos’s time dependency in remote access contexts—a common trap is assuming the VPN or RADIUS configuration is faulty, when the real culprit is a simple time mismatch. Remember the memory tip: “Kerberos hates a clock that’s off by a tick,” so always check time synchronization first when VPN users can reach other resources but fail to authenticate.
SSCP Access Controls Practice Question
This SSCP practice question tests your understanding of access controls. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
You are the security administrator for a healthcare organization that uses a Windows Active Directory domain. The organization has recently implemented a new electronic health record (EHR) system that requires users to authenticate before accessing patient data. The EHR system uses Kerberos for authentication. Users report that they can access the EHR system from their office workstations, but when they attempt to access it remotely via VPN, they receive an 'Access Denied' error. The VPN uses RADIUS for authentication and assigns IP addresses from a separate subnet. The EHR server is in the same domain as the workstations. You verify that the users are able to connect to the VPN successfully and can access other internal resources. What is the most likely cause of the issue?
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
✓
The remote user's system clock is not synchronized with the domain controller.
Kerberos authentication is highly sensitive to time skew; the default maximum tolerance is 5 minutes (RFC 4120). When users connect via VPN, their system clocks may drift from the domain controller's time, especially if they are not synchronized with the domain's time source. This time difference causes Kerberos to reject the ticket request, resulting in an 'Access Denied' error even though the VPN connection itself is successful.
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.
✗
The EHR server is not joined to the domain.
Why it's wrong here
The server is in the same domain, otherwise office access would fail.
✗
The VPN does not forward Kerberos traffic to the domain controller.
Why it's wrong here
Other resources are accessible, so Kerberos traffic is likely forwarded.
✓
The remote user's system clock is not synchronized with the domain controller.
Why this is correct
Kerberos requires time sync; VPN issues often corrupt time sync.
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.
✗
The user's account is not in the EHR application's access group.
Why it's wrong here
Users can access from office, so group membership is correct.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates focus on network connectivity or VPN configuration (like port forwarding) rather than the time synchronization requirement of Kerberos, assuming that successful VPN connection implies all authentication protocols will work seamlessly.
Detailed technical explanation
How to think about this question
Kerberos relies on the authenticator timestamp to prevent replay attacks; if the client's clock differs from the KDC's clock by more than the configured skew (default 5 minutes in Windows), the KDC returns a KRB_AP_ERR_SKEW error. VPN clients often use their local system time, which may not be synchronized with the domain's time source (e.g., via NTP). This is a common issue in remote access scenarios where the client is not domain-joined or does not have the domain's time source configured.
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 analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Access Controls — This question tests Access Controls — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The remote user's system clock is not synchronized with the domain controller. — Kerberos authentication is highly sensitive to time skew; the default maximum tolerance is 5 minutes (RFC 4120). When users connect via VPN, their system clocks may drift from the domain controller's time, especially if they are not synchronized with the domain's time source. This time difference causes Kerberos to reject the ticket request, resulting in an 'Access Denied' error even though the VPN connection itself is successful.
What should I do if I get this SSCP 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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. A Windows workstation is unable to authenticate to a Kerberos-based application. The time on the workstation is 5 minutes ahead of the domain controller. What is the impact?
hard
A.The user would be prompted for credentials but authentication would proceed
✓ B.Authentication will fail because the time difference exceeds the default Kerberos clock skew limit
C.Only NTLM authentication would be affected
D.No impact; Kerberos can tolerate up to 10 minutes of skew
Why B: Kerberos authentication relies on timestamps to prevent replay attacks. The default maximum clock skew allowed between a client and a domain controller is 5 minutes (as defined in RFC 4120). Since the workstation is exactly 5 minutes ahead, it meets the threshold, but any additional delay or network latency can cause the timestamp to exceed the limit, resulting in authentication failure. Therefore, the user will be unable to authenticate.
Last reviewed: Jun 11, 2026
Question Discussion
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This SSCP 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 SSCP exam.
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