Unseen Threats: Demystifying Fileless Malware Attacks

Written by Mitchell Langley

September 8, 2023

Unseen Threats: Demystifying Fileless Malware Attacks

In today’s digital landscape, cybersecurity is a critical concern for organizations of all sizes. Malicious actors are constantly evolving their tactics to bypass traditional security measures. One such technique that has gained significant traction is deploying fileless malware.

Unlike traditional malware that relies on executable files, fileless malware operates in memory, making it difficult to detect and eradicate. In this article, we will explore the key aspects of fileless malware attacks, including their characteristics, stages, working mechanisms, and strategies to detect and prevent them.

Key Differences Between Traditional Malware and Fileless Malware

Traditional malware typically relies on executable files that are stored on disk. These files are detectable by antivirus software and can be removed by deleting or quarantining them. On the other hand, fileless malware operates entirely in memory, leaving no trace on the disk. It utilizes legitimate system processes and tools to carry out its malicious activities, making it challenging to detect and mitigate.

Examples of Fileless Malware Attacks

Fileless malware attacks have become increasingly prevalent in recent years. Some notable examples include the PowerShell-based attacks, such as the Kovter and Emotet malware, and the use of living off-the-land techniques by the APT29 group. These attacks have demonstrated the sophistication and effectiveness of fileless malware in bypassing traditional security measures.

How Fileless Malware Works

Fileless malware operates in a stealthy manner, making it difficult to detect and eradicate. Understanding its working mechanisms is crucial in developing effective countermeasures.

Memory-Based Execution

Fileless malware leverages legitimate processes already present in the system’s memory to execute its malicious code. By exploiting vulnerabilities in these processes or by using scripting languages like PowerShell, the malware can run undetected and carry out its malicious activities.

Living Off the Land Techniques

Fileless malware often utilizes built-in system tools and legitimate applications to carry out its activities. By abusing these tools, such as Windows Management Instrumentation (WMI), or macros in office documents, the malware can execute commands and perform actions without raising suspicion.

Fileless Persistence Mechanisms

To ensure persistence, fileless malware utilizes various techniques that do not rely on traditional file-based methods. It may leverage the Windows registry to store its code or configuration, making it difficult to detect. The malware may also hide within system services, taking advantage of their elevated privileges to maintain persistence and evade detection.

Stages of a Fileless Malware Attack

A fileless malware attack typically involves several stages, each serving a specific purpose in the attacker’s overall objective.

Stage 1: Initial Infection Vector

The initial infection vector is the entry point for the malware into the target system. Attackers may exploit vulnerabilities in software or operating systems, or they may employ social engineering techniques, such as phishing emails or malicious downloads, to trick users into executing the malware.

In 2017, a fileless malware variant known as “Dridex” used these techniques. Attackers sent phishing emails with infected attachments that contained macros. When the victim opened the document and enabled macros, the malware was executed in memory, leaving no traditional file traces on the system.

Stage 2: Establishing Persistence

Once inside the system, the malware establishes persistence to ensure its longevity. It achieves this by employing memory-based techniques, such as injecting malicious code into legitimate processes, or by manipulating the Windows registry to execute the malware during system startup.

Lazarus Group, a North Korean state-sponsored hacking group used fileless malware designed for macOS to target banks, financial institutions and cryptocurrency. They injected malicious code into legitimate applications running in memory. This allowed them to maintain control over the compromised systems, monitor financial transactions, and siphon off crypto funds over an extended period without being detected.

Stage 3: Command and Control Communication

After establishing persistence, the malware establishes communication with a command and control (C&C) server operated by the attacker. This communication allows the attacker to send commands to the malware and receive information or updates. To evade detection, fileless malware often uses DNS tunneling or encrypted communication channels to mask its activities.

Stage 4: Expanding the Attack Surface

In this stage, the malware seeks to expand its reach within the network. It may employ lateral movement techniques to propagate to other systems, taking advantage of vulnerabilities or weak security measures. Additionally, the malware may employ privilege escalation techniques to gain higher levels of access and control within the network.

In 2017, the “Astaroth” fileless malware campaign targeted users in Brazil and Europe. Astaroth initially infected systems through malicious email attachments or links. Once inside a system, it used living-off-the-land techniques, leveraging legitimate Windows processes and tools, to move laterally within the network.

Detecting and Preventing Fileless Malware Attacks

Given the stealthy nature of fileless malware attacks, detecting and preventing them requires a multi-layered approach that combines endpoint protection, network security measures, and user awareness.

Endpoint Protection Strategies

Behavior-based detection is a crucial component of endpoint protection against fileless malware. By monitoring system activities and looking for suspicious or abnormal behavior, security solutions can detect and block fileless malware attacks. Application whitelisting, which allows only trusted applications to run on a system, can also help prevent the execution of fileless malware.

Network Security Measures

Intrusion detection/prevention systems (IDS/IPS) play a vital role in detecting and blocking fileless malware communication with C&C servers. In addition, network segmentation, which separates critical systems and sensitive data from the rest of the network, can limit the lateral movement capabilities of fileless malware.

User Awareness and Training

Educating users about the risks of fileless malware and providing training on identifying phishing emails and suspicious behavior is crucial in preventing successful attacks. Encouraging users to report any suspicious activity or potential security incidents can help security teams respond quickly to mitigate the impact of fileless malware attacks.

Regular Software Updates and Patch Management

Keeping software and operating systems up-to-date with the latest patches and security updates is essential in mitigating the risk of fileless malware attacks. Many threat actors exploit known vulnerabilities that have already been patched by software vendors.

Monitoring and Analysis of System Logs

Monitoring and analyzing system logs can provide valuable insights into potential fileless malware attacks. Anomalies or suspicious activities in system logs can indicate the presence of fileless malware. Implementing a robust log management and analysis system can help detect and respond to fileless malware attacks timely.

Incident Response and Recovery Planning

Having a well-defined incident response plan in place is crucial for effectively responding to fileless malware attacks. This plan should encompass various stages to address the evolving nature of these threats:

Detection and Identification: Implement robust monitoring and detection systems capable of spotting fileless malware behavior. Recognizing the signs early is essential.

Isolation and Containment: In the event of an infection, swiftly isolate infected systems from the network to prevent further lateral movement.

Forensic Analysis: Conduct a thorough forensic analysis to understand the extent of the breach, the malware’s behavior and the vulnerabilities exploited. This insight helps in fine-tuning defenses.

System Restoration: In case of an attack, use clean backups to restore affected systems to a known good state. Ensure that the restored systems have been thoroughly checked for any remaining malware artifacts.

Regular Testing and Updates: Periodically test and update the incident response plan to ensure its effectiveness against the evolving threat landscape. Conduct drills and simulations to train staff on proper response procedures.

Backup and Disaster Recovery: Maintaining secure and up-to-date backups is critical. Regularly back up critical data and systems to offline or isolated storage. This ensures that even if systems are compromised, clean backups can always be used for recovery.

Backup and Disaster Recovery Considerations

Backup Frequency: Regularly back up critical data and system configurations. Frequent backups reduce the risk of data loss in case of an attack.

Air-Gapped Storage: Store backups in an isolated air-gapped environment that is not directly accessible from the network. This prevents malware from reaching and compromising backup data.

Versioning: Maintain multiple versions of backups. This enables recovery to a point in time before the infection occurred, reducing data loss.

Data Encryption: Encrypt backup data with AES 256-bit encryption to protect it from unauthorized access, including potential attackers trying to manipulate or delete backups.

Testing Recovery Procedures: Periodically test the restoration process from backups to ensure it works as intended. Identify and address any issues in the recovery workflow.

Disaster Recovery Planning: Develop a comprehensive disaster recovery plan that outlines the steps and responsibilities for restoring critical systems and operations in the event of a successful fileless malware attack.


In an era where digital threats constantly evolve, fileless malware attacks loom as a formidable menace for organizations, regardless of their size. These stealthy adversaries can sidestep conventional security defenses, making them a cause for concern. However, understanding the intricacies of fileless malware is the first step toward fortifying your defenses. By taking a proactive approach, you can significantly reduce the risk of falling victim to these insidious attacks.

Related Articles

Stay Up to Date With The Latest News & Updates

Join Our Newsletter


Subscribe To Our Newsletter

Sign up to our weekly newsletter summarizing everything thats happened in data security, storage, and backup and disaster recovery

You have Successfully Subscribed!