Microsoft Sentinel SOC 101: How to Detect and Mitigate Fileless Malware Attacks with Microsoft Sentinel

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Fileless malware is a type of malicious software that does not rely on executable files to infect and compromise a system. Instead, it uses legitimate programs, scripts, or memory to execute malicious code and evade detection by traditional antivirus solutions. Fileless malware attacks are on the rise, and they pose a serious threat to organizations of all sizes and industries.

In this post, I will explain what fileless malware is, how it works, and how you can use Microsoft Sentinel, a cloud-native security information and event management solution, to detect and mitigate fileless malware attacks across your enterprise.

What is Fileless Malware?

Fileless malware is a memory-based malicious software component that lives in random access memory (RAM) instead of the hard drive. It uses built-in components of an operating system, such as Windows PowerShell, Windows Management Instrumentation (WMI), or Microsoft Office macros, to turn a computer against itself. Fileless malware can also leverage web browsers, JavaScript, or Adobe Flash to inject malicious code into web pages or documents.

Fileless malware attacks are stealthy and sophisticated, as they do not leave any traces on the disk that can be scanned by antivirus products. They also take advantage of trusted applications and processes that are often whitelisted by security tools. Fileless malware can perform various malicious activities, such as data exfiltration, credential theft, ransomware encryption, or lateral movement within a network.

How Does Fileless Malware Work?

Fileless malware attacks can be initiated by various methods, such as phishing emails, malicious downloads, or compromised websites. The common factor is that they do not require the user to download or run any malicious files. Instead, they exploit vulnerabilities or features of legitimate programs to execute malicious code in memory.

For example, a phishing email may contain a link or an attachment that looks legitimate but actually contains a PowerShell script that runs in the background when clicked. The script may then download additional payloads from a remote server or use WMI to execute commands on other machines in the network.

Another example is a malicious website that uses JavaScript or Flash to inject code into the web browser’s memory. The code may then access sensitive information stored in the browser, such as cookies or passwords, or redirect the user to another malicious site.

How Can Microsoft Sentinel Help?

Microsoft Sentinel is a cloud native SIEM solution powered by AI and automation that delivers intelligent security analytics across your entire enterprise. With Microsoft Sentinel, you can:

• Collect data at cloud scale across all users, devices, applications, and infrastructure, both on-premises and in multiple clouds.

• Detect previously uncovered threats and minimize false positives using analytics and unparalleled threat intelligence from Microsoft.

• Investigate threats with AI and hunt suspicious activities at scale, tapping into decades of cybersecurity work at Microsoft.

• Respond to incidents rapidly with built-in orchestration and automation of common tasks.

Microsoft Sentinel can help you detect and mitigate fileless malware attacks by using the following features:

• Data connectors: Microsoft Sentinel comes with many connectors for Microsoft and non-Microsoft solutions that provide real-time integration. You can also use common event format (CEF), Syslog, or REST-API to connect your data sources with Microsoft Sentinel. By collecting data from various sources, you can gain visibility into your entire environment and identify potential indicators of fileless malware activity.

• Workbooks: Microsoft Sentinel integrates with Azure Monitor workbooks to create interactive reports and dashboards that visualize your data. You can use workbooks to monitor key metrics and trends related to fileless malware attacks, such as PowerShell usage, WMI events, browser activity, or network connections.

• Analytics rules: Microsoft Sentinel uses analytics rules to correlate alerts from different sources and generate incidents for investigation. You can use built-in analytics rules or create your own custom rules to detect fileless malware attacks based on specific criteria or patterns. For example, you can create a rule that triggers an incident when a PowerShell script downloads an executable file from an external domain.

• Playbooks: Microsoft Sentinel leverages Azure Logic Apps to automate and orchestrate common tasks for incident response. You can use playbooks to perform actions such as blocking malicious IPs or domains, isolating infected machines, sending notifications, or creating tickets. For example, you can create a playbook that runs when an incident related to fileless malware is detected and executes the following steps:

  • Send an email notification to the security team with the incident details.

  • Block the IP address or domain associated with the fileless malware attack using Azure Firewall or another firewall solution.

  • Isolate the infected machine from the network using Azure Security Center or another endpoint protection solution.

  • Create a ticket in your IT service management system with the incident information.

Preventing Fileless Malware Attacks

Some possible ways to prevent fileless malware attacks are:

• Use web filtering to block phishing emails that may contain malicious links or attachments that can introduce fileless malware into your system.

See: Microsoft Sentinel SOC 101: How to Detect and Mitigate Phishing Attacks with Microsoft Sentinel

• Use managed threat hunting to monitor your system for suspicious activity and behavior that may indicate the presence of fileless malware. You can hire an experienced company that can locate and mitigate fileless malware for you or use a managed threat hunting service to continuously monitor your system and stop fileless malware from spreading or completing the attack sequence.

  • Microsoft Sentinel: Hunting in Microsoft Sentinel is the process of proactively looking for security threats and malicious behaviors in your environment, using powerful search and query tools. Hunting can help you find undetected threats, validate your hypotheses, and improve your detection coverage. The following Hunting query example determines emails sent by top malicious/bad IP addresses:

let cutoff = 5;
EmailEvents
| where ThreatTypes has "Malware" or ThreatTypes has "Phish"
| summarize count() by SenderIPv4
| where count_ > cutoff // Arbitrary cutoff, increase or decrease as needed
| join EmailEvents on SenderIPv4  
| where DeliveryAction =~ "Delivered"

• Use indicators of attack (IOAs) analysis to detect fileless malware based on its actions rather than its file signatures. You can look for abnormal code execution, lateral movements, data exfiltration, and other malicious activities that can trigger a scan. Then you can start fileless malware mitigation steps, such as scanning the command lines of trusted applications that may be corrupted by fileless malware.

  • Microsoft Sentinel: Threat intelligence in Microsoft Sentinel is the ability to quickly pull threat intelligence from various sources and use it to detect and respond to known threats in your environment. Threat intelligence can help you provide essential context to unusual activity, so you can take action to protect your systems and users.

Summary

Fileless malware is a serious threat that can evade traditional antivirus solutions and compromise your systems and data. To protect your enterprise from fileless malware attacks, you need a modern SIEM solution that can collect, analyze, and respond to security events across your environment. Microsoft Sentinel is a cloud native SIEM solution that provides intelligent security analytics and threat response powered by AI and automation. With Microsoft Sentinel, you can detect and mitigate fileless malware attacks and improve your security posture. To learn more about Microsoft Sentinel, visit the official website or the documentation.

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