Pass CAS-004 Exam Guide

A regular expression (regex) is a sequence of characters that defines a search pattern for matching text. A regex can be used to detect the presence of a malicious piece of software communicating with its command-and-control server by matching the indicators of compromise (IOC) in the network traffic.

In this case, the systems administrator should use the regex Host: [a-z]*.malicious.com to determine if any of the company hosts are compromised, while reducing false positives, because this regex would:

Match the Host header in the HTTP request, which specifies the domain name of the command-and-control server.

Allow any subdomain under the malicious.com domain, by using the character class [a-z]*, which matches zero or more lowercase letters.

Escape the dot character in the domain name, by using the backslash , which prevents it from being interpreted as a wildcard that matches any character.

Not match any other parts of the IOC that could change, such as the URL path, the User-Agent header, or the HTTP method.

Input validation is a technique that checks the user input for any errors, malicious data, or unexpected values before processing it by the application. Input validation can prevent many common web application attacks, such as:

SQL injection, which exploits a vulnerability in the application’s database query to execute malicious SQL commands.

Cross-site scripting (XSS), which injects malicious JavaScript code into the application’s web page to execute on the client-side browser.

Directory traversal, which accesses files or directories outside of the intended scope by manipulating the file path.

In this case, the security engineer should recommend input validation as the best mitigation technique, because it would:

Prevent the exfiltration of a company report by validating the file parameter in the URL and ensuring that it matches a predefined list of allowed files or formats.

Enhance the security of the web application by filtering out any malicious or invalid input from users or attackers.

Be more effective and efficient than other techniques, such as firewall, WAF (Web Application Firewall), or DLP (Data Loss Prevention), which may not be able to detect or block all types of web application attacks.

The security analyst acknowledges this alert because it is a false positive. A false positive is an event classification that indicates a benign or normal activity is mistakenly flagged as malicious or suspicious by the SIEM system. A false positive can occur due to misconfigured rules, outdated signatures, or faulty algorithms. A false positive can waste the security analyst’s time and resources, so it is important to acknowledge and dismiss it after verifying that it is not a real threat. Verified References:

https://www.ibm.com/topics/siem

https://www.microsoft.com/en-us/security/business/security-101/what-is-siem

https://www.splunk.com/en_us/data-insider/what-is-siem.html