Pass the CompTIA CompTIA CySA+ CS0-003 Questions and answers with CertsForce

Aplaybookprovides astep-by-stepguide for handling specific types of incidents like ransomware, making it invaluable during triage. It outlines predefined procedures, aiding consistent and fast decision-making.

The incident response plan (A) provides high-level structure.

Lessons learned (B) applyafterthe incident.

Tabletop exercises (D) are training tools, not live guides.

???? Reference: Chapple & Seidl, CySA+ Practice Tests, Incident Response, Chapter 3 – Playbooks and Procedures​.

???? Objective: 3.1 - Apply incident response procedures based on an incident classification​.

Registry artifacts and EDR data are two data sources that can provide valuable information about the root cause of a malware outbreak. Registry artifacts can reveal changes made by the malware to the system configuration, such as disabling security services, modifying startup items, or creating persistence mechanisms1. EDR data can capture the behavior and network activity of the malware, such as the initial infection vector, the command and control communication, or the lateral movement2. These data sources can help the analyst identify the malware family, the attack technique, and the threat actor behind the outbreak.

The correct answer is D because random-looking DNS requests can indicate malware using a domain generation algorithm (DGA) for command-and-control, but the analyst should first validate the suspicious domains using threat intelligence or reputation sources. The scenario asks what should be done first to determine whether Host X has been compromised, so enrichment and validation of the domain indicators is the best first step.

Exact supporting extract: the All-in-One CySA+ guide explains that malware may use DGAs for command-and-control exchanges and that high-entropy domains often look like gibberish to humans. It also warns that DGAs may have legitimate uses in content delivery networks, so additional analysis is needed to reduce false positives.

The same guide defines a DGA as a threat actor technique used to generate domain names rapidly using seemingly random but predictable processes so malware can eventually connect with command-and-control infrastructure.

Why the other options are incorrect:

A is incorrect because allowing the domains before validation may permit command-and-control or data exfiltration.

B is incorrect because reinstalling the software does not determine whether the DNS domains are malicious or legitimate.

C is incorrect because blocking all outbound connections is a containment action, not the best first investigative step.

D is correct because threat intelligence helps validate whether the suspicious domains are known malicious infrastructure or legitimate generated domains.

D ( " grnail.com " ) is a suspicious domain that resembles " gmail.com. "

The high " bytes out " value (525,984 bytes) indicates potential data exfiltration.

Attackers often use typosquatting (e.g., " grnail.com " instead of " gmail.com " ) to trick users into visiting malicious sites.

Why Not Other Options?

A (Netflix, B YouTube, C TikTok) → Large downloads, but expected behavior for streaming sites.

E (Google Translate) → Low data volume, no exfiltration risk.

F (Office.com) → Microsoft service, no indication of malicious activity.

Awareness training and education are essential to help staff recognize phishing emails and understand safe email practices, particularly when using legacy applications that might not have the latest securityfeatures. Training helps build a culture of security mindfulness, which is critical for preventing social engineering attacks. According to CompTIA Security+ and CySA+ frameworks, user education is a fundamental aspect of organizational defense against phishing. Options like replacing applications or implementing MFA (while helpful) do not directly address the need for user awareness in this scenario.

To determine the correct priority, you must filter the options by applying the rules from Security Policy 1006 in the order of importance dictated by the scenario.

“The Company shall prioritize patching of publicly available systems and services over patching of internally available system.”

Option A: Internal System

Option B: External System (Keep)

Option C: External System (Keep)

Option D: Internal System

Result: Eliminate Options A and D. We are now choosing between B and C.

“In situations where a choice must be made between confidentiality and availability, the Company shall prioritize confidentiality of data over availability of systems and data.”

To apply this, you must read the CVSS v3.1 Vector String for the remaining options. The relevant metrics are C (Confidentiality) and A (Availability).

Option B (CAP.SHIELD): C:H / I:N / A:N

Confidentiality: High (C:H)

Availability: None (A:N)

Interpretation: This vulnerability allows for a significant breach of data confidentiality.

Option C (LOKI.DAGGER): C:N / I:N / A:H

Confidentiality: None (C:N)

Availability: High (A:H)

Interpretation: This vulnerability allows for a significant disruption of service (DoS).

Conclusion: Since the policy explicitly prioritizes Confidentiality (Option B) over Availability (Option C), Option B is the highest priority.

The exam expects you to parse raw CVSS strings to assess risk. Here is the breakdown for the correct answer (Option B):

Metric

Code

Value

Meaning

AV

AV:N

Network

The vulnerability is exploitable remotely via the network (most dangerous).

AC

AC:L

Low

No complex conditions are required to exploit.

PR

PR:N

None

No privileges are required (unauthenticated).

UI

UI:N

None

No user interaction is required.

C

C:H

High

Confidentiality Impact. Total loss of confidentiality.

A

A:N

None

Availability Impact. No impact to uptime.

Comprehensive and Detailed Step-by-Step Explanation:Performing a vulnerability scan during the recovery phase ensures that corrective actions, such as patches or configuration changes, have effectively addressed the vulnerabilities exploited during the incident. This step validates the system’s security before fully restoring operations.

The suspicious line in the web server logs is an attempt to execute a command on the server, indicating a command injection attack.References: CompTIA CySA+ Study Guide: Exam CS0-003, 3rd Edition, Chapter 5, page 197; CompTIA CySA+ CS0-003 Certification Study Guide, Chapter 5, page 205.

The endpoint log entry shows that a new account named “admin” has been created on a Windows system with a local group membership of “Administrators”. This indicates that a new account has been introduced on the system with administrative privileges. This could be a sign of malicious activity, such as privilege escalation or backdoor creation, by an attacker who has compromised the system.

The analyst should review PID 768 first because it is the parent process of another suspicious process (PID 1100) and it is also highly suspicious itself due to its unexpected file path.

Why PID 768 is the best first process to review

Path anomaly (strong IoC): Legitimate Windows binaries like calc.exe and cmd.exe are normally found in trusted OS directories (e.g., C:\Windows\System32\). In the table, both CALC.exe and CMD.exe appear in a user’s Documents folder (C:\Users\JDoe\Documents\...). That is a classic sign of masquerading (a malicious binary using a legitimate-sounding name). The All-in-One guide explicitly describes how attackers disguise malicious processes by using legitimate-sounding names and mimicking system processes.

Parent-child relationship (investigation priority): PID 1100 (Documents\CMD.exe) is suspicious, but it is a child of PID 768 (Documents\CALC.exe). Investigating the parent first helps you understand what spawned the suspicious child, what activity preceded it, and whether PID 768 is the root of the execution chain. The All-in-One guide highlights that analysts should examine process parent-child relationships and investigate unexpected dependencies as a way to detect malicious activity:Exact extract (All-in-One Exam Guide): “Analyze process dependencies Examine process parent-child relationships and investigate any unexpected or unusual dependencies that may indicate malicious activity.” It also emphasizes monitoring grandparent/parent/child relationships to detect deviations from normal process hierarchies:Exact extract (All-in-One Exam Guide): “Monitoring the relationships between processes, particularly grandparent, parent, and child relationships, can be a valuable method for detecting unusual activity.”

Abused/LOLBIN context: cmd.exe is a commonly abused Windows utility in attacks. The Sybex Study Guide notes that attackers often abuse built-in tools and that abnormal OS process behavior involving tools like cmd.exe can indicate compromise:Exact extract (Sybex Study Guide): “For Windows systems, a handful of built-in tools are most commonly associated with attacks like these, including cmd.exe…”

Why the other options are less correct

A (533) and B (740) are running from C:\Windows\System32\... which is the expected location for legitimate Windows binaries in normal circumstances, so they’re less suspicious than the copies running from a user Documents folder.

D (1100) is suspicious, but it is a child of PID 768. Investigating 768 first helps determine the origin and execution chain that led to the suspicious cmd instance.

References (CompTIA CySA+ CS0-003 documents / study guides used):

Mya Heath et al., CompTIA CySA+ All-in-One Exam Guide (CS0-003): parent/child process dependency analysis; process hierarchy monitoring; masquerading techniques

Mike Chapple & David Seidl, CompTIA CySA+ Study Guide (CS0-003): abnormal OS process behavior; cmd.exe commonly associated with attacks