mediumMultiple ChoiceObjective-mapped
ISC2 CC Practice Question: Refer to the exhibit
Exhibit
Refer to the exhibit. === syslog output === Jan 15 09:23:45 firewall01 %ASA-4-106023: Deny tcp src outside:192.0.2.10/3456 dst inside:10.0.0.5/22 by access-group "OUTSIDE_IN" [0x0, 0x0] Jan 15 09:23:46 firewall01 %ASA-4-106023: Deny tcp src outside:192.0.2.10/3457 dst inside:10.0.0.5/23 by access-group "OUTSIDE_IN" [0x0, 0x0] Jan 15 09:23:47 firewall01 %ASA-4-106023: Deny tcp src outside:192.0.2.10/3458 dst inside:10.0.0.5/80 by access-group "OUTSIDE_IN" [0x0, 0x0] Jan 15 09:23:48 firewall01 %ASA-4-106023: Deny tcp src outside:192.0.2.10/3459 dst inside:10.0.0.6/22 by access-group "OUTSIDE_IN" [0x0, 0x0] Jan 15 09:23:49 firewall01 %ASA-4-106023: Deny tcp src outside:192.0.2.10/3460 dst inside:10.0.0.6/23 by access-group "OUTSIDE_IN" [0x0, 0x0]
Refer to the exhibit. A security analyst is reviewing firewall logs and notices repeated denied TCP packets from 192.0.2.10 to internal hosts. The packets are being denied by the access-group "OUTSIDE_IN". What is the most likely reason for these denials?
⚠ Common exam trap
ISC2 often tests the distinction between a port scan and a DoS attack, where candidates mistakenly choose DoS because they see 'repeated denied packets' without recognizing the pattern of multiple destinations versus a single target flood.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
An external host is performing a port scan against internal systems.
The repeated denied TCP packets from 192.0.2.10 (an external IP) to multiple internal hosts indicate a port scan. The access-group 'OUTSIDE_IN' is applied to the outside interface, and the firewall is denying these packets because they match a deny ACE (access control entry) that blocks unsolicited inbound traffic. This pattern of multiple denied connections from a single external source to different internal destinations is characteristic of a reconnaissance scan, not a DoS attack or data exfiltration.
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 external host is performing a port scan against internal systems.
Why this is correct
The sequential source ports and different destination ports across multiple hosts indicate a scan.
- ✗
The firewall is misconfigured and blocking legitimate traffic.
Why it's wrong here
There is no indication of legitimate traffic; the pattern suggests scanning.
- ✗
An internal host has been compromised and is exfiltrating data.
Why it's wrong here
Exfiltration would show outbound traffic, not inbound denied packets.
- ✗
An external host is launching a denial-of-service (DoS) attack.
Why it's wrong here
DoS attacks typically flood a single port, not scan multiple ports and hosts.
Visual reference
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Related to this question
Learn chapter
Introduction to Security Principles
Key term
Group
A group is a collection of users, devices, or other objects that are assigned permissions and policies together for simplified management in identity and governance systems like Microsoft Entra ID.
Key term
Access control
Access control is the security practice of determining who or what is allowed to view, use, or enter a resource, and under what conditions.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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