- A
Revert the web server to a previous snapshot from before the suspected compromise date, then run a full antivirus scan on the restored system.
Why wrong: Reverting to a snapshot may not remove a kernel rootkit that persists across boots if it is stored outside the snapshot (e.g., in a dedicated partition). Also, antivirus scans often miss custom APT malware, and this does not preserve evidence properly.
- B
Perform a live forensic analysis of the PHP application logs and database to identify the specific vulnerability used, then apply a hotfix to the application code.
Why wrong: While code review is important, this approach ignores the kernel rootkit and does not contain or eradicate the APT foothold. The attacker may have other persistence mechanisms beyond the application.
- C
Isolate the web server from the network immediately, capture a full disk and memory image, then reimage the server from a trusted backup or OS image, and restore application data from a known clean backup.
Isolation stops the active reverse shell and lateral movement. Imaging preserves evidence of the rootkit and attacker activities. Reimaging ensures the kernel module and any other persistence are removed.
- D
Block the external IP address at the firewall and block all outbound traffic from the web server except to specific internal IPs, then continue monitoring for other compromised hosts.
Why wrong: Blocking the IP is reactive and does not clean the compromised server. The attacker could use another C2 address. This approach fails to eradicate the threat and risks leaving a backdoor operational.
CS0-003 Incident Response and Management Practice Question
This CS0-003 practice question tests your understanding of incident response and management. 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 a senior incident responder for a large technology company. During a routine threat hunting exercise, you detect unusual network traffic from a Linux web server to an external IP address that is known to be associated with an advanced persistent threat (APT) group. The web server runs a custom PHP application and is not in the DMZ; instead, it's on the internal network serving a management dashboard. You have captured a memory dump of the web server and analyzed it with volatility. The output shows a suspicious process running with the name 'apache2' but with an invalid parent process (PID 1 is 'apache2' itself). Additionally, you find a kernel module loaded called 'hideproc.ko' that is not part of the standard kernel. The network connections show a reverse shell to the external IP. You need to determine the most effective containment and eradication strategy that minimizes data loss and maintains business continuity while preserving evidence for law enforcement involvement.
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
Isolate the web server from the network immediately, capture a full disk and memory image, then reimage the server from a trusted backup or OS image, and restore application data from a known clean backup.
Option C is correct because the presence of a kernel rootkit ('hideproc.ko') and a reverse shell indicates deep, persistent compromise that cannot be cleaned by patching or scanning. Isolating the server preserves volatile evidence (memory, disk) for law enforcement, while reimaging from a trusted backup ensures complete removal of the attacker's foothold, minimizing data loss and restoring business continuity.
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.
- ✗
Revert the web server to a previous snapshot from before the suspected compromise date, then run a full antivirus scan on the restored system.
Why it's wrong here
Reverting to a snapshot may not remove a kernel rootkit that persists across boots if it is stored outside the snapshot (e.g., in a dedicated partition). Also, antivirus scans often miss custom APT malware, and this does not preserve evidence properly.
- ✗
Perform a live forensic analysis of the PHP application logs and database to identify the specific vulnerability used, then apply a hotfix to the application code.
Why it's wrong here
While code review is important, this approach ignores the kernel rootkit and does not contain or eradicate the APT foothold. The attacker may have other persistence mechanisms beyond the application.
- ✓
Isolate the web server from the network immediately, capture a full disk and memory image, then reimage the server from a trusted backup or OS image, and restore application data from a known clean backup.
Why this is correct
Isolation stops the active reverse shell and lateral movement. Imaging preserves evidence of the rootkit and attacker activities. Reimaging ensures the kernel module and any other persistence are removed.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Block the external IP address at the firewall and block all outbound traffic from the web server except to specific internal IPs, then continue monitoring for other compromised hosts.
Why it's wrong here
Blocking the IP is reactive and does not clean the compromised server. The attacker could use another C2 address. This approach fails to eradicate the threat and risks leaving a backdoor operational.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may choose a containment-only option (D) or a patch-only option (B) because they underestimate the persistence of kernel-level rootkits, failing to recognize that eradication requires complete reimaging from a trusted source.
Detailed technical explanation
How to think about this question
The 'hideproc.ko' kernel module likely hooks system calls (e.g., sys_getdents or sys_kill) to hide its own process from user-space tools like ps or top, making traditional detection ineffective. A reverse shell using a modified 'apache2' binary with PID 1 as its parent suggests the attacker replaced the legitimate init process or used a technique like LD_PRELOAD injection to masquerade as Apache. In real-world APT scenarios, such rootkits can also intercept network packets via netfilter hooks, so firewall rules alone are insufficient.
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 team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this CS0-003 question test?
Incident Response and Management — This question tests Incident Response and Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Isolate the web server from the network immediately, capture a full disk and memory image, then reimage the server from a trusted backup or OS image, and restore application data from a known clean backup. — Option C is correct because the presence of a kernel rootkit ('hideproc.ko') and a reverse shell indicates deep, persistent compromise that cannot be cleaned by patching or scanning. Isolating the server preserves volatile evidence (memory, disk) for law enforcement, while reimaging from a trusted backup ensures complete removal of the attacker's foothold, minimizing data loss and restoring business continuity.
What should I do if I get this CS0-003 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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