What Is Fileless Malware? How It Works and How to Stop It

Malware has been around for decades, disrupting systems and stealing data in countless ways. However, as cybersecurity defenses become more sophisticated, so do the threats. One of the newest and most sophisticated types to emerge is fileless malware. Unlike traditional malware that installs harmful files on your computer, fileless attacks operate directly in memory, making them harder to detect and stop.

Over the past few years, these attacks have become increasingly common, targeting businesses of all sizes and leaving minimal traces behind. If you want to understand how fileless malware works, why it’s so dangerous, and what you can do to protect your organization, keep reading.

What Is Fileless Malware?

Fileless malware is a type of malicious code that operates entirely in the memory of a computer system without creating any files on the hard drive. Traditional malware, such as viruses, trojans, and computer worms, rely on files to infect and spread across a system. 

In contrast, fileless malware resides in the system’s RAM, registry, and other volatile storage areas, making it difficult to detect using conventional antivirus software.

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How Does Fileless Malware Work?

Malware that doesn’t use files operates by entering your computer’s memory. Hence, no harmful code ever makes it onto your hard drive. It enters your system in a strikingly similar manner to that of other malicious software.

For example, a hacker may deceive a victim into clicking on a link or attachment in a phishing email. To induce the victim to click on the attachment or link, the attacker may utilize social engineering to play on their emotions. Afterward, the malware enters your system and spreads from one device to another.

Attackers can access data they can either steal or exploit to obstruct an organization’s activities using fileless malware. Fileless malware conceals itself using tools that system administrators would typically trust, including Windows scripting tools or PowerShell. 

They are frequently included in a company’s allowlist of applications. Fileless malware corrupts a trustworthy program, making it more challenging to detect than malicious software that lives in a separate file on your hard disc.

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Common Fileless Malware Examples

Over the years, several fileless malware attacks have made headlines for their stealth and sophistication. Here are some of the most notable examples:

1. Astaroth (Guildma): Astaroth is a notorious fileless malware strain that primarily targets financial institutions and government organizations in Latin America and Europe. It spreads through malicious links or phishing emails and utilizes legitimate Windows tools, such as WMIC and PowerShell, to execute commands directly in memory. By relying on trusted system utilities, it avoids triggering traditional antivirus defenses.
2. Kovter: Originally developed as a click-fraud malware, Kovter evolved into a fully fileless threat capable of persistence even after system reboots. It hides its malicious code within the Windows registry, allowing it to execute commands without storing files on disk. Kovter has been used to deliver ransomware and ad-fraud campaigns, mostly targeting businesses through phishing and malicious ads.
3. PowerGhost: PowerGhost is a cryptojacking malware that infects corporate networks to mine cryptocurrency using victims’ computing resources. It spreads through exploits and remote administration tools, leveraging PowerShell and Windows Management Instrumentation (WMI) for execution. Its ability to run entirely in memory allows it to operate silently and remain undetected for long periods.
4. Poweliks: Poweliks was one of the first known examples of truly fileless malware. It stores its payload in the Windows registry and utilizes legitimate system processes to execute malicious activities, such as downloading additional malware or stealing data. Its stealth and persistence techniques set the stage for future fileless attacks.

Fileless Malware Attack Chain

As fileless malware operates in memory and makes use of trusted technologies, signature-based antivirus software, and intrusion detection systems frequently mistake it for benign software.

Due to its ability to work covertly, sustain persistence, and go unnoticed by target organizations lacking the necessary tools, it essentially renders them oblivious to a continuing intrusion.

Enterprises’ reliance on signature-based solutions to protect their networks is a key factor encouraging CTAs to launch fileless malware attacks against networks.

Types of Fileless Malware

Here’s how Fileless Malware spreads because of various types:

1. Memory-based fileless malware is the most common type of fileless malware, which resides in the system’s RAM and other volatile storage areas.
2. Script-based fileless malware uses scripting languages, such as PowerShell or JavaScript, to execute malicious code in the memory of a target system.
3. Macro-based fileless malware uses macros embedded in documents, such as Microsoft Office files or PDFs, to execute malicious code in the memory of a target system.
4. Registry-based fileless malware resides in the system’s registry, a database that stores configuration information for the operating system and installed software.

How to Detect Fileless Malware

Detecting fileless malware is challenging because it does not leave the usual signs of infection. There are no suspicious files stored on the disk, and no clear installation trails are evident. These attacks run directly in system memory and utilize legitimate tools, such as PowerShell, WMI, or macros, to remain undetected. Traditional antivirus software often fails to detect them because it focuses on scanning files for known signatures.

Modern cybersecurity tools employ various strategies that focus on behavioral analysis, memory activity, and real-time monitoring, rather than static file analysis.

Behavioral Analysis: This method observes how programs behave, rather than searching for specific malware signatures. It alerts security teams when it detects unusual actions, such as a Word document attempting to run PowerShell commands or scripts trying to establish unauthorized network connections.

Memory Scanning: Since fileless malware operates in RAM, memory scanning tools inspect system memory to look for suspicious code or injected processes. This helps identify and stop threats that are active only in memory before they can cause harm.

Endpoint Detection and Response (EDR): EDR solutions monitor endpoints in real time and collect data on system events and user activity. They utilize analytics and threat intelligence to identify abnormal behavior, isolate infected devices, and promptly alert security teams.

Using these advanced detection methods allows organizations to identify fileless threats even when there are no files to scan. Regular antivirus software is not enough to stop them, so behavior-based detection is now essential for modern cybersecurity.

Stages of a Fileless Attack

The following are steps that an attacker may take during a fileless attack:

Initial Access

The attacker gains initial access to the target network through phishing or other social engineering techniques.

Execution

The attacker delivers the malicious code to one or more computers in the target network using several techniques (such as through an email attachment). The malicious code runs in memory without touching the disk. This makes it difficult for antivirus software to detect the attack and prevent it from succeeding.

Persistence

The attackers install tools (for example, PowerShell scripts) that allow them to maintain access to the network even after they have left their initial point of entry or after their initial malware has been removed from all infected devices.

These tools can be used to execute attacks against the same network while remaining undetected by antivirus software because they do not leave any traces on disk or in memory once they have completed their task of installing new malware components or performing other tasks that require administrative rights on targeted systems.

Objectives

Once an attacker has established persistence on a victim’s machine, he can start working towards his ultimate objective: stealing data or money from victims’ bank accounts, exfiltrating sensitive data, or other nefarious activities.

The objectives of a fileless attack are often very similar to those of traditional attacks: steal passwords, steal credentials, or otherwise gain access to systems within a network; exfiltrate data from a network; install ransomware or other malware on systems; execute commands remotely; and so forth.

How to Protect Against Fileless Malware?

Now you must be worried about how you can save yourself from this severe threat. Here’s how you can be on the safe side:

• Keep your software up to date: Fileless malware relies on exploiting vulnerabilities in legitimate software applications. Keeping your software updated with the latest security patches and updates can help prevent attackers from exploiting known vulnerabilities.
• Use antivirus software: While traditional antivirus software may not be effective against fileless malware, specialized endpoint protection solutions, such as behavior-based detection or application control, can help detect and prevent fileless malware attacks.
• Use least privilege: Fileless malware often requires administrative privileges to execute attacks. Using the principle of least privilege, which limits user access to the minimum level required to perform their job, can help reduce the impact of fileless malware attacks.
• Implement network segmentation: Network segmentation involves dividing a network into smaller, isolated segments, each with its security policies and access controls. Implementing network segmentation can help contain the spread of fileless malware attacks, limiting their impact on the organization.

Conclusion

Fileless malware is a highly sophisticated cyber attack that poses a significant threat to computer systems and networks. Unlike traditional malware, fileless malware operates entirely in the memory of a target system, making it challenging to detect and remove using conventional antivirus software. 

To protect against fileless malware, it is essential to keep software up to date, use specialized endpoint protection solutions, implement the principle of least privilege, and employ network segmentation. As cyber threats evolve, it is crucial to stay informed about the latest attack techniques and take proactive measures to safeguard our data and systems.

Email also remains one of the most common entry points for fileless malware and phishing attacks. Protecting your email domain with PowerDMARC can help prevent attackers from impersonating your organization and launching fileless payloads through malicious emails. With advanced DMARC, SPF, and DKIM enforcement, PowerDMARC helps you stop threats before they reach your inbox.

Frequently Asked Questions

Can fileless malware be removed?

Yes, but it’s harder to remove than traditional malware. Because it runs in memory, traces often vanish after a reboot. Advanced EDR tools, full system scans, and security updates are necessary to completely eradicate the infection.

Is fileless malware common?

Yes. Fileless attacks are becoming increasingly frequent as hackers seek ways to evade antivirus tools. Businesses of all sizes are seeing a steady rise in these stealthy threats.

How does fileless malware spread?

It often spreads through phishing emails, malicious links, or infected documents. Once opened, it utilizes built-in Windows tools, such as PowerShell or WMI, to run directly in memory and transfer across systems.

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Ahona Rudra

Domain & Email Security Expert at PowerDMARC

Ahona is the Marketing Manager at PowerDMARC, with 5+ years of experience in writing about cybersecurity topics, specializing in domain and email security. Ahona holds a post-graduation degree in Journalism and Communications, solidifying her career in the security sector since 2019.

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