The answer is selective authentication, which restricts which accounts from a trusted forest can access resources in the trusting forest. This design choice directly mitigates privilege escalation in cross-forest trusts by preventing a compromised domain in one forest from automatically gaining broad access; instead, only explicitly authorized accounts are allowed through. On the CompTIA SecurityX CAS-004 exam, this concept tests your understanding of how to layer defenses beyond default SID filtering—a common trap is assuming SID filtering alone is sufficient, but selective authentication adds a critical constraint at the resource level. Remember the memory tip: “Selective stops the spread”—it ensures that even if an attacker compromises a forest, they cannot escalate privileges across the trust unless their account is on the approved list.
CAS-004 Security Architecture Practice Question
This CAS-004 practice question tests your understanding of security architecture. 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.
An organization plans to establish a cross-forest trust between two Active Directory forests to enable resource access. The security architect is concerned about the risk of privilege escalation from a compromised domain in one forest. Which design choice best mitigates this risk?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Why wrong: SID filtering prevents elevation of privilege but does not limit which accounts can authenticate; selective authentication is more granular.
D
Use selective authentication and restrict the authorized accounts
Selective authentication ensures only specified users can access resources in the trusting forest, limiting exposure from a compromise.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use selective authentication and restrict the authorized accounts
Using selective authentication restricts what resources users from the trusting forest can access, ensuring that only specified accounts are allowed. Forest-level authentication would allow broader access. SID filtering is enabled by default for cross-forest trusts but is not sufficient alone; selective authentication provides an additional constraint. Disabling the trust is not practical.
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.
✗
Remove the trust entirely and use individual local accounts
Why it's wrong here
This would break the access requirement and is not a security-architecture decision.
✗
Configure the trust to use forest-wide authentication instead of selective
SID filtering prevents elevation of privilege but does not limit which accounts can authenticate; selective authentication is more granular.
✓
Use selective authentication and restrict the authorized accounts
Why this is correct
Selective authentication ensures only specified users can access resources in the trusting forest, limiting exposure from a compromise.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Authentication checks who the user is.
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
What to study next
Got this wrong? Here's your next step.
Review Cisco AAA concepts — authentication, authorization, and accounting. Study privilege levels (0–15), command authorization under TACACS+, and how RADIUS differs. Then practise related CAS-004 questions on access control and AAA configuration.
Security Architecture — This question tests Security Architecture — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: Use selective authentication and restrict the authorized accounts — Using selective authentication restricts what resources users from the trusting forest can access, ensuring that only specified accounts are allowed. Forest-level authentication would allow broader access. SID filtering is enabled by default for cross-forest trusts but is not sufficient alone; selective authentication provides an additional constraint. Disabling the trust is not practical.
What should I do if I get this CAS-004 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 CAS-004 questions on access control and AAA configuration.
Are there clue words in this question I should notice?
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Authentication checks who the user is.
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