The correct answer is SSH access is allowed from any source, as this firewall rule exposes TCP port 22 to the entire internet, creating a critical firewall misconfiguration. Permitting SSH from any IP dramatically increases the attack surface, making the network vulnerable to automated brute-force attacks, credential stuffing, and unauthorized access attempts, since attackers can scan for open port 22 from anywhere. On the CompTIA SecurityX CAS-004 exam, this scenario tests your ability to identify overly permissive access control entries (ACEs) in a border firewall rule set, a common trap where examinees overlook the “any source” parameter while focusing on the allowed service. A frequent memory tip is to remember that SSH should always be restricted to specific management IPs or a VPN gateway—never left open to the wild. Think of it as “lock the back door, don’t leave the key under the mat.”
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.
Exhibit
access-list 100 permit tcp any any eq 22
access-list 100 permit tcp host 10.0.0.10 any eq 443
access-list 100 permit tcp 192.168.1.0 0.0.0.255 any eq 80
access-list 100 deny ip any any
Refer to the exhibit. A security analyst reviews the following firewall rule on a border firewall. Which vulnerability is present?
access-list 100 permit tcp any any eq 22
access-list 100 permit tcp host 10.0.0.10 any eq 443
access-list 100 permit tcp 192.168.1.0 0.0.0.255 any eq 80
access-list 100 deny ip any any
A
HTTPS is only allowed from a single host
Why wrong: This is a secure configuration, not a vulnerability.
B
SSH access is allowed from any source
Permitting SSH from any source exposes the server to unauthorized access attempts.
C
HTTP is allowed from the internal network
Why wrong: This is an intended design for internal users.
D
An implicit deny rule is missing
Why wrong: An explicit deny ip any any is present, so no implicit deny issue.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
SSH access is allowed from any source
Option A is correct because the rule permits SSH (TCP/22) from any source, increasing the risk of brute-force attacks. Option B describes a legitimate restrictive rule for HTTPS. Option C is an intended internal network rule for HTTP. Option D is incorrect because an explicit deny all is present at the end.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
HTTPS is only allowed from a single host
Why it's wrong here
This is a secure configuration, not a vulnerability.
✓
SSH access is allowed from any source
Why this is correct
Permitting SSH from any source exposes the server to unauthorized access attempts.
Related concept
Standard ACLs match source addresses.
✗
HTTP is allowed from the internal network
Why it's wrong here
This is an intended design for internal users.
✗
An implicit deny rule is missing
Why it's wrong here
An explicit deny ip any any is present, so no implicit deny issue.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
Got this wrong? Here's your next step.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related CAS-004 ACL questions on filtering logic and placement.
Security Engineering — This question tests Security Engineering — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: SSH access is allowed from any source — Option A is correct because the rule permits SSH (TCP/22) from any source, increasing the risk of brute-force attacks. Option B describes a legitimate restrictive rule for HTTPS. Option C is an intended internal network rule for HTTP. Option D is incorrect because an explicit deny all is present at the end.
What should I do if I get this CAS-004 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related CAS-004 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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