Fileless Malware – What is It, How Does it Work, & How to Prevent it?

Written By Sambita Panigrahy  
Anuraag Singh
Approved By Anuraag Singh 
Published On October 30th, 2023
Reading Time 8 Minutes Reading

Unlike traditional malware, fileless malware doesn’t require attackers to sneak malicious code into the victim’s computer. Rather it uses a computer system’s built-in tools to execute a cyberattack. That means it takes advantage of the security loopholes present in installed software to execute an attack. Thus, it becomes extremely difficult to detect this kind of malware which makes it very dangerous.

Here in this blog, we’ll cover what exactly fileless malware is, how hackers use it, and most importantly how can you detect & prevent it.

Without further ado, let’s start our discussion.

Background Information on Fileless Malware

Fileless malware first came to light in 2017 as a mainstream cyberattack but these have been around for a while. It is a type of malicious software that uses authorized tools as a medium to infect a computer. The main concern is that it doesn’t rely on files and leaves no digital footprint behind. Therefore, making it challenging to detect and erase.

Today, adversaries are becoming more sophisticated and they are aware of the strategies that organizations follow to defend themselves. Consequently, they (attackers) come up with new and advanced hacking techniques that evade the existing defense systems of the organization.

But, the question is what are the common fileless malware techniques that hackers use? Let’s have a look at those.

Common Fileless Malware Methods Used by Hackers

Although fileless malware attacks don’t require the installation of any code, access to the environment is still required so that attackers can alter the environment’s native tools to their liking. There are numerous techniques to get access and launch assaults and they are as follows.

1. Exploit Kits

Code fragments, command sequences, or data collections make up exploits and exploit kits are collections of exploits. These tools are used by adversaries to exploit flaws in installed software or operating systems that are known to exist.

Exploits can be injected straight into memory without needing to write anything to the disc, making them an effective approach to conducting a fileless malware attack. They can be used by adversaries to automate first compromises at a large scale.

Regardless of whether the assault is fileless or makes use of conventional malware, an exploit always starts in the same manner. A victim is typically seduced using social engineering or a phishing email. The majority of the time, the exploit kit also comes with a management console that the attacker can utilize to take over the system. A customized exploit can sometimes be created and launched immediately after the targeted system has been scanned for vulnerabilities using the exploit kit.

2. Registry Resident Malware

Malware that installs itself in the Windows registry in order to remain undetected and persistent is known as registry resident malware.

The most common method of infecting Windows PCs is to use dropper software to download a malicious file. This malicious file stays active on the targeted system, leaving it open to antivirus software detection. While using a dropper application, fileless malware does not download a harmful file. Instead, malicious code is directly written into the Windows registry by the dropper software itself.

The harmful code is buried in native files that are immune to AV detection, so it may be written to run each time the OS is launched. Additionally, there is no malicious file that could be found.

3. Memory-Only Malware

Malware that exists solely in memory does so. The Duqu worm is an illustration of memory-only malware that can go unnoticed since it only exists in memory. There are two versions of Duqu 2.0; the first is a backdoor that enables the enemy to infiltrate an organization. The opponent can then employ Duqu 2.0’s enhanced version, which comes with extra functions like data exfiltration, lateral movement, and reconnaissance. Companies in the telecom sector and at least one well-known security software vendor have both been breached using Duqu 2.0.

4. Fileless Ransomware

Adversaries don’t just focus on one kind of attack. They take advantage of any technology that will aid in the payload’s capture. Attackers of ransomware now use fileless methods to insert harmful code into documents using native scripting languages like macros or to write the code straight into memory via an exploit. Without ever writing a single line to disc, the ransomware encrypts hostage files by commandeering native programs like PowerShell.

5. Hijacked Credentials

Attackers may launch a fileless attack using stolen credentials to get access to their target while posing as a genuine user. Once entered, the attacker can carry out their assault using native tools like Windows Management Instrumentation (WMI) or PowerShell. They can create user accounts that give them access to any machine they want or they can build persistence by burying code in the kernel or the registry.

How Are Fileless Malware Attacks Executed?

Adversaries execute fileless malware attacks in a structured manner and they do that in four steps.

Step-1: Gain Access: Attackers gain remote access (by using web scripting) to the victim’s system, to establish a beachhead for their attack. They do that by remotely exploiting a vulnerability.

Step-2: Steal Login Details: After gaining access, attackers will try to steal credentials for the compromised environment so that can easily come and go whenever they like.

Step-3: Maintain Continuity: The attackers modify the registry to create a backdoor. They do so so that they do not have to repeat the initial steps.

Step-4: Exfiltrate Data: In this final step, attackers prepare for data exfiltration. They use a file system and built-in compression utility to gather data after that upload the data through FTP.

fileless malware

Techniques to Detect Fileless Malware

Surprisingly, classic anti-virus programs, allow listing, sandboxing, and in fact, machine learning methods fail to protect against fileless malware attacks. So, it would be appropriate for organizations to take an integrated approach that combines multiple methods. Such as:

  • Indicators of Attack (IoA): It’s one of the best approaches against fileless malware attacks. This method looks for signs, for instance, code execution, lateral movement, and actions that seem to be intended to clock their true intent. IoAs examine intent, context, and sequences, so they can detect and block malicious activities that are performed using a legitimate account.
  • Deploy Managed Threat Hunting: The gathering and normalization of extensive amounts of data is an essential part of threat hunting. Though it is a time-consuming and laborious task yet it is a necessary component in a defense that protects against fileless malware.

Managed threat-hunting/cybersecurity services could monitor the organization’s IT environment around the clock to proactively search for intrusion and recognize subtle activities that may go unnoticed by common technologies.

How SysTools Can Help Organizations Prevent Fileless Malware Attacks?

As discussed earlier, detecting fileless malware is quite a challenging task. However, SysTools’ proven Managed Cybersecurity Service is the best fit for organizations. The security team delivers a powerful & integrated approach to secure your organization’s endpoints and prevent further probable cyberattacks. 

For more details, contact our team now!


Q- What is a fileless malware?

Malicious programs known as “fileless malware” don’t rely on conventional files kept on a computer’s hard disc. Rather, it runs in memory, carrying out its malicious operations through authorized system tools and processes.

Q- How can malware without a file operate?

Usually, a vulnerability or social engineering assault allows fileless malware to enter a system. It executes its malicious code directly in memory once inside by using scripts, macros, or reputable system utilities like PowerShell or Windows Management Instrumentation (WMI).

Q- What are the typical ways that malware without files gets distributed?

Malicious links, drive-by downloads, phishing emails, and software flaws are some of the ways that fileless malware can spread. Social engineering assaults are also frequent; they lure victims into executing scripts.

Q- How dangerous are malware files without a file?

Due to its lack of file creation, fileless malware can be extremely nimble and challenging to identify. All the while avoiding conventional antivirus and endpoint security, it is capable of data theft, system takeover, monitoring, and enabling more attacks.

Q- How can assaults using fileless malware be avoided?

Advanced security technologies that track system activity, measure network traffic, and check memory utilization are necessary for the detection of fileless malware. Malicious or odd activity can be found with the aid of behavior-based anomaly detection and endpoint security methods.

Q- What are a few instances of fileless malware attacks in the real world?

The Emotet banking Trojan, the PowerShell Empire post-exploitation framework, and different APT (Advanced Persistent Threat) campaigns that use fileless techniques for data theft and espionage are examples of fileless malware attacks.

Q- Can any operating system be infected by fileless malware?

Linux, macOS, and Windows are just a few of the operating systems that fileless malware can target. However, because Windows is so widely used in business settings, it is frequently targeted.