サーバー1は、サポート終了となったオペレーティングシステムであるWindows Server 2008 R2を実行しています。このオペレーティングシステムはMicrosoftからのセキュリティパッチの提供が終了しているため、非常に脆弱です。さらに、この古いOS上でMicrosoft IISを実行していることで、リスクはさらに高まります。ウイルス対策ソフトウェアはインストールされていますが、この古いOSは、サポートされているオペレーティングシステム上で稼働している他のシステムと比較して、はるかに深刻な脅威ベクトルとなります。
参照：
Chapple & Seidl,CompTIA CySA+ Study Guide(Sybex, 2023), Chapter 7: "Missing Patches" section highlights that outdated operating systems should be prioritized for remediation due to critical vulnerabilities

A digital certificate is a document that contains the public key and identity information of a web server, and is signed by a trusted third-party authority called a certificate authority (CA). A digital certificate allows the web server to establish a secure connection with the clients using the HTTPS protocol, and also verifies the authenticity of the web server. A self-signed certificate is a digital certificate that is not signed by a CA, but by the web server itself. A self-signed certificate can cause issues with the website, as it may not be trusted by the clients or their browsers. Clients may receive warnings or errors when trying to access the website, indicating that the site could not be trusted or that the connection is not secure. Official Reference:
https://www.comptia.org/blog/the-new-comptia-cybersecurity-analyst-your-questions-answered
https://partners.comptia.org/docs/default-source/resources/comptia-cysa-cs0-002-exam-objectives
https://www.techtarget.com/searchsecurity/quiz/Sample-CompTIA-CySA-test-questions-with-answers

A new program has been set to execute on system start is the most likely cause of the suspicious activity that is occurring, as it indicates that the malware has modified the registry keys of the system to ensure its persistence. File Integrity Monitoring (FIM) is a tool that monitors changes to files and registry keys on a system and alerts the security analyst of any unauthorized or malicious modifications. The alert triggered by FIM shows that the malware has created a new registry key under the Run subkey, which is used to launch programs automatically when the system starts. The new registry key points to a file named "update.exe" in the Temp folder, which is likely a malicious executable disguised as a legitimate update file. Official References:
* https://www.comptia.org/blog/the-new-comptia-cybersecurity-analyst-your-questions-answered
* https://partners.comptia.org/docs/default-source/resources/comptia-cysa-cs0-002-exam-objectives
* https://www.comptia.org/training/books/cysa-cs0-002-study-guide

インシデント対応プレイブックは、セキュリティインシデントへの対応に関する体系的なステップバイステップガイドを提供します。特定の脅威指標やイベントが発生した際に取るべきアクションを定義し、協調的かつ一貫性のある対応を実現します。

The security analyst is validating a Local File Inclusion (LFI) vulnerability, as indicated by the "/.../.../.../" in the GET request which is a common indicator of directory traversal attempts associated with LFI. The other options are not relevant for this purpose: SQL injection involves injecting malicious SQL statements into a database query; XSS involves injecting malicious scripts into a web page; CSRF involves tricking a user into performing an unwanted action on a web application.