An employee clicks on a seemingly harmless link in an email. No file is downloaded, no attachment is opened, everything looks normal. But in the background, a PowerShell script is launched directly in the working memory. No traces on the hard drive, no alarm from the virus scanner. Access remains undetected for weeks until sensitive data suddenly appears on the network and systems are encrypted.
No download, no file, no obvious clue, and yet the system is infected. Fileless malware takes a different approach to traditional malware. It works in secret, directly in the working memory, uses existing system processes, and leaves hardly any traces. Fileless malware is one of the most insidious forms of malware because it often leaves no classic files on the hard drive, but instead uses legitimate system processes and tools such as wscript.exe, cscript.exe, mshta.exe, or powershell.exe to execute malicious code directly in the working memory. Those who rely on antivirus programs that only search for suspicious files often realize too late that someone has already gained access. One click on a harmless-looking link can be enough, and the rest happens invisibly. This is precisely what makes this form of attack so dangerous and so fascinating.
How do fileless attacks happen?
Fileless malware often enters the system through a chain of inconspicuous events. It usually starts with a classic attack vector: a phishing email, a prepared link, or a manipulated website. As soon as a user clicks on it, a script starts in the background – often through PowerShell, WMI, or other legitimate system tools.
The script loads the malicious code directly into the working memory and executes it from there. Since no files are saved, conventional protection mechanisms such as virus scanners often remain blind to the attack. As a result, the attacker can execute commands, steal data, download additional malware, or take over entire systems—all without leaving a single suspicious file behind.
Risks
- Difficult to detect: No classic files means fewer signatures and hardly any traces for antivirus scanners.
- Misuse of legitimate tools: It uses PowerShell, WMI, scripts, and other system processes, making it appear like “normal” activity.
- Works in memory: No permanent files means it can disappear on reboot and still cause damage.
- Highly adaptable: Attackers can tailor it to specific environments and targets.
- Late detection: It often goes undetected for weeks or months, during which time it can steal data, manipulate it, or sabotage systems.
- High consequential damage: From data leaks and extortion to complete system takeover, the consequences are often serious.
- Difficult forensic analysis: Without file traces, investigations and evidence preservation become a challenge.
Our tips
- Up-to-date systems and patches: Keep your operating system, applications, and security tools up to date.
- Restrict PowerShell and scripts: Only allow signed scripts and configure PowerShell as restrictively as possible and regulate it via group policies. Special tools or registry entries can also be used to assign or legitimize known script handlers in order to prevent misuse at an early stage.
- Advanced endpoint security: Rely on modern EDR/XDR solutions that monitor behavior in memory and processes.
- Least privilege principle: Only grant user and administrative rights to the extent necessary to prevent misuse.
- Employee training: Recognize and report phishing and social engineering early on.
- Application whitelisting: Only known, approved applications may be executed.
- Continuous monitoring: Set up early alerts for anomalies such as unusual PowerShell commands, WMI requests, or other suspicious process calls.
- Regular backups: Back up data and store it offline so you can respond quickly in the event of an attack.
Conclusion
Fireless malware shows how quickly and silently modern attacks can occur. It exploits what is already there, thereby breaking through familiar security concepts. To stop it in its tracks, you need a keen eye, modern defense strategies, and people who remain vigilant. Because those who see the invisible stay one step ahead.