The correct answers are enabling SELinux in enforcing mode and applying kernel hardening via sysctl, as these directly mitigate privilege escalation by enforcing mandatory access controls and reducing the kernel attack surface. SELinux confines processes to the least privilege necessary, preventing a compromised service from escalating to root or accessing unauthorized resources, while sysctl parameters like kernel.kptr_restrict and kernel.dmesg_restrict block common information disclosure and memory manipulation vectors. On the CompTIA SecurityX CAS-004 exam, this question tests your ability to distinguish between practical hardening and overly restrictive measures that break functionality—a common trap is assuming all SUID bits must be removed, which would cripple essential system commands. Remember the mnemonic “SEAL the kernel”: SELinux Enforcing and sysctl Adjustments for Least privilege.
CAS-004 Security Engineering Practice Question
This CAS-004 practice question tests your understanding of security engineering. 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.
A security engineer is hardening a Linux server. Which TWO of the following are best practices for preventing privilege escalation attacks?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Apply kernel hardening with sysctl
Options B and E are correct. SELinux (B) provides mandatory access control that restricts processes, and kernel hardening with sysctl (E) reduces the attack surface. Option A is incorrect because removing all SUID bits may break essential system functionality. Option C is incorrect because disabling all non-root user accounts is impractical and violates least privilege. Option D is incorrect because restricting cron jobs to root only is not directly related to privilege escalation prevention.
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.
✗
Disable all user accounts except root
Why it's wrong here
Disabling all non-root accounts is impractical and violates least privilege.
✓
Apply kernel hardening with sysctl
Why this is correct
Kernel hardening parameters (e.g., disabling IP forwarding) reduce attack surface.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✓
Enable SELinux in enforcing mode
Why this is correct
SELinux provides mandatory access control, limiting the impact of privilege escalation.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Authentication checks who the user is.
✗
Remove the SUID bit from all binaries
Why it's wrong here
Removing all SUID bits may break system functions; it is too restrictive.
✗
Restrict cron jobs to root only
Why it's wrong here
This does not directly prevent privilege escalation and may limit automation.
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 Engineering — This question tests Security Engineering — Authentication checks who the user is..
What is the correct answer to this question?
The correct answer is: Apply kernel hardening with sysctl — Options B and E are correct. SELinux (B) provides mandatory access control that restricts processes, and kernel hardening with sysctl (E) reduces the attack surface. Option A is incorrect because removing all SUID bits may break essential system functionality. Option C is incorrect because disabling all non-root user accounts is impractical and violates least privilege. Option D is incorrect because restricting cron jobs to root only is not directly related to privilege escalation prevention.
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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