Quarantining the server is the best action to perform immediately, as it isolates the affected server from the rest of the network and prevents the ransomware from spreading to other systems or data. Quarantining the server also preserves the evidence of the ransomware attack, which can be useful for forensic analysis and law enforcement investigation. The other actions are not as urgent as quarantining the server, as they may not stop the ransomware infection, or they may destroy valuable evidence. Shutting down the server may not remove the ransomware, and it may trigger a data deletion mechanism by the ransomware. Reimaging the server may restore its functionality, but it will also erase any traces of the ransomware and make recovery of encrypted data impossible. Updating the OS to the latest version may fix some vulnerabilities, but it will not remove the ransomware or decrypt the data. Official References:
* https://www.cisa.gov/stopransomware/ransomware-guide
* https://www.cisa.gov/sites/default/files/publications/Ransomware_Executive_One- Pager_and_Technical_Document-FINAL.pdf
* https://www.cisa.gov/stopransomware/ive-been-hit-ransomware

The function that can be used on a shell script to identify anomalies on the network routing most accurately is:
function x() { info=(dig(dig -x $1 | grep PTR | tail -n 1 | awk -F ".in-addr" '{print $1} ' ).origin.asn.cymru.
com TXT +short) & & echo "$1 | $info" }
This function takes an IP address as an argument and performs two DNS lookups using the dig command. The first lookup uses the -x option to perform a reverse DNS lookup and get the hostname associated with the IP address. The second lookup uses the origin.asn.cymru.com domain to get the autonomous system number (ASN) and other information related to the IP address. The function then prints the IP address and the ASN information, which can help identify any routing anomalies or inconsistencies

Header analysis is the technique of examining the metadata of an email, such as the sender, recipient, date, subject, and routing information. It can help to identify the source of a malicious email by revealing the IP address and domain name of the originator, as well as any spoofing or redirection attempts. References:
CompTIA CySA+ Study Guide: Exam CS0-003, 3rd Edition, Chapter 6, page 240; CompTIA CySA+ CS0-
003 Certification Study Guide, Chapter 6, page 249.

The correct answer is D because the analyst should first validate whether the suspicious DNS domains are malicious or legitimate. Random-looking DNS domains may indicate malware using a domain generation algorithm (DGA) for command-and-control, but they can also appear in legitimate services such as content delivery networks or software update mechanisms. Therefore, the best first step is to enrich the DNS indicators using threat intelligence and reputation sources.
Exact supporting extract: the CySA+ All-in-One guide explains that DNS tunneling and abnormal DNS queries may be used for command-and-control or exfiltration. It also states that high-entropy domains appear random or "gibberish" to humans and that malware may use DGAs for C2 communication. However, it also warns that computer-generated domain names can have legitimate uses in content delivery networks.
The same guide explains that threat research should help answer questions such as whether an artifact is benign, whether anyone has seen it before, and why it is present in the system. It further explains that reputation data for domains, URLs, and IP addresses helps determine whether activity is associated with malware, phishing, C2, or data exfiltration.
Why the other options are incorrect:
A is incorrect because allowing the domains without validation could permit C2 or data exfiltration.
B is incorrect because reinstalling the software does not determine whether the DNS activity is malicious.
C is incorrect because blocking all outbound connections is a containment action, not the best first investigative step when the analyst is still determining whether compromise occurred.
D is correct because threat intelligence/reputation lookup is the most appropriate first validation step for suspicious DNS indicators.

Zero Trust Network Access (ZTNA)simplifies secure remote access to cloud and SaaS applications by enforcing identity-based, least-privilege access policies. It eliminates the need to extend traditional network- based access models to the cloud. ZTNA ensures thateach user is verified continuouslyregardless of their network location, aligning perfectly with complex multi-cloud or SaaS environments.
* RADIUS (A)is an older authentication protocol, not ideal for SaaS cloud scale.
* SDN (B)controls network flow, not identity management.
* SWG (D)is a secure web proxy, not for access control and IAM extension.
#Reference:
* CS0-003 Exam Objectives 1.1 - Identity and Access Management
* Sybex Study Guide - Chapple & Seidl, Chapter 2: Zero Trust & Cloud IAM