Fileless Malware

Simple Definition for Beginners:

Fileless malware is a type of malicious software that operates in computer memory without leaving traditional file traces on disk, making it harder to detect and remove using traditional antivirus or security tools.

Common Use Example:

A fileless malware attack infiltrates a system through malicious scripts in legitimate processes, evading antivirus detection and executing malicious actions directly in memory, such as stealing sensitive data or launching further attacks.

Technical Definition for Professionals:

Fileless malware, also known as memory-based or non-persistent malware, is a stealthy cyber threat that exploits vulnerabilities in software, operating systems, or applications to execute malicious code directly in computer memory (RAM) without relying on persistent files or executables stored on disk.

Fileless malware attacks leverage legitimate system tools, scripts, processes, or memory-resident payloads to evade detection, bypass security controls, and carry out malicious activities. Key characteristics and techniques of fileless malware include:

• Memory Injection: Injecting malicious code or payloads into running processes, system memory, or vulnerable applications to execute commands, download additional payloads, hijack system functions, or perform stealthy actions without creating files on disk.
• PowerShell Attacks: Leveraging PowerShell, a legitimate scripting language on Windows systems, to execute malicious scripts, download payloads from remote servers, establish command-and-control (C2) communications, escalate privileges, or manipulate system configurations.
• Living-off-the-Land (LotL): Abusing built-in system utilities, administrative tools, Windows Management Instrumentation (WMI), Windows Registry, PowerShell, or

legitimate applications to blend with normal system activities and avoid detection by traditional signature-based antivirus solutions.

• Script-Based Attacks: Using JavaScript, VBScript, batch files, macros, or other scripting languages embedded in documents, emails, or web pages to deliver and execute malicious code directly in memory, exploiting vulnerabilities in software or exploiting human behaviors (e.g., phishing).
• Exploit Kits: Exploiting software vulnerabilities, zero-day exploits, or known vulnerabilities in browsers, plugins, or applications to deliver fileless payloads, gain unauthorized access, execute remote code, or compromise systems without leaving traces on disk.
• In-Memory Persistence: Establishing persistence mechanisms in memory, such as scheduled tasks, registry entries, or malicious services, to ensure re-infection or continued control of compromised systems after reboots or security scans.
• Anti-Forensic Techniques: Employing anti-analysis, anti-debugging, anti-sandboxing, or anti-virtualization techniques to evade security research, malware analysis, reverse engineering, and forensic investigations by security professionals or incident responders.
• Stealthy Operations: Conducting stealthy operations, data theft, lateral movement, privilege escalation, credential theft, cryptocurrency mining, or data exfiltration directly in memory, minimizing the footprint and visibility of malicious activities on disk.

Fileless malware poses significant challenges to traditional cybersecurity defenses, requiring advanced detection techniques, behavior-based analysis, endpoint security solutions, and proactive threat hunting to identify and mitigate memory-based threats effectively.