The term “file-less malware” has become a cybersecurity buzzword, often accompanied by dramatic claims about attacks that exist purely in memory without touching the disk. While this technology represents a significant evolution in attack techniques, the terminology has created a dangerous misconception: that file-less attacks don’t involve malicious files at all.

This misunderstanding has real consequences for security teams who might underestimate the importance of file-based defenses when dealing with so-called “file-less” threats. Let’s examine why this terminology is misleading and what it means for defensive strategies.

What “File-less” Actually Means

File-less malware doesn’t mean an attack operates without any files whatsoever. Instead, it refers to malware that doesn’t persistently store its main payload as a traditional executable file on the target system’s hard drive. The malicious code primarily operates in memory, using legitimate system processes and tools to carry out its objectives.

However, this narrow definition obscures a crucial reality: file-less attacks almost always begin with, or involve, malicious files at some stage of the attack lifecycle.

The File-less Attack Lifecycle: Files Are Still There

Let’s trace through a typical file-less attack to see where files actually appear:

Initial Delivery

Most file-less attacks begin with a file delivery mechanism:

• Malicious email attachments: Word documents with malicious macros, PDFs with embedded exploits, or ZIP files containing droppers
• Infected downloads: Legitimate-looking software installers, browser plugin updates, or document files
• USB-based attacks: Files placed on removable media that initiate the attack chain

Exploitation Phase

Even when the main payload runs in memory, the attack often involves:

• Dropper files: Small executable files that download and execute the main payload
• Script files: PowerShell, JavaScript, or VBScript files that facilitate the attack
• Configuration files: Files containing command-and-control server addresses, encryption keys, or attack parameters

Persistence and Lateral Movement

File-less malware frequently creates files for:

• Registry manipulation scripts: Files that modify system settings for persistence
• Credential harvesting tools: Temporary files used to extract and exfiltrate passwords
• Lateral movement utilities: Files transferred between systems during network propagation

Real-World Examples

Emotet: Often labeled as file-less, Emotet typically begins with malicious Word documents containing macros. While the main payload operates in memory, the initial infection vector is decidedly file-based.

Cobalt Strike: This penetration testing tool, frequently misused by attackers, can operate file-lessly but often involves PowerShell scripts, beacon configuration files, and various utilities that exist as files during different phases of the attack.

Living-off-the-Land attacks: These leverage legitimate system tools like PowerShell, WMI, and PsExec in malicious ways. While the tools themselves are legitimate, attackers often use malicious scripts and configuration files to control these tools.

Why This Distinction Matters for Security

The “file-less” label has led some organizations to deprioritize file-based security controls, assuming they’re less relevant against modern threats. This is a critical error for several reasons:

File-Based Defenses Remain Crucial

• Email security gateways can catch malicious attachments before they reach users
• Endpoint detection systems can identify suspicious file creation patterns
• Application control can prevent unauthorized script execution
• Content disarm and reconstruction (CDR) can neutralize malicious files before they’re opened

Early Detection Opportunities

Since many file-less attacks begin with files, robust file security provides opportunities for early detection and prevention—before the attack transitions to its memory-resident phase.

Comprehensive Defense Strategy

Modern threats require layered defenses that address both file-based and memory-based attack vectors. Focusing exclusively on memory protection while neglecting file security creates dangerous gaps.

Recommendations for Security Teams

1. Maintain robust file security: Don’t reduce investment in email security, endpoint protection, and file analysis tools because of file-less threat concerns.
2. Implement comprehensive monitoring: Monitor both file system activity and memory-based processes for signs of malicious activity.
3. Focus on attack chains: Understand that most attacks involve multiple phases, including file-based components, even when the main payload is file-less.
4. User education: Train users to recognize malicious files, as they often represent the initial attack vector for file-less malware.
5. Behavioral analysis: Implement security tools that can detect suspicious behavior patterns, regardless of whether they originate from files or memory-resident processes.

Conclusion

The cybersecurity industry’s adoption of the “file-less malware” terminology, while technically accurate in describing certain attack techniques, has created a misleading impression that files are no longer relevant to these threats. In reality, malicious files remain a critical component of most attack chains, even those ultimately classified as file-less.

Security teams should resist the temptation to view file-less attacks as purely memory-based phenomena that don’t require file-focused defenses. Instead, they should recognize that comprehensive security requires protecting against both file-based and memory-based threats as part of an integrated defense strategy.

The most effective approach to combating modern malware—whether labeled file-less or not—is a layered security strategy that addresses threats at every stage of the attack lifecycle, including the file-based components that are often present even in supposedly file-less attacks.

Remember: just because an attack is called “file-less” doesn’t mean your file security can take a coffee break.