Shellcode Loaders and Common Evasion Patterns

Shellcode Loaders and Common Evasion Patterns - article cover image Malware & C2
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Disclaimer: This article is provided strictly for educational purposes and authorized security testing. Only run these techniques against systems you own or have explicit written permission to assess. Unauthorized access to computer systems is illegal in virtually every jurisdiction and can carry severe penalties.

Introduction

Shellcode loaders stage and execute payloads while evading static and dynamic analysis.

Encryption, syscalls, and sleep obfuscation are common patterns.

How It Works

Loaders decrypt payloads at runtime and execute them via allocation and indirect calls.

Direct syscalls bypass user-mode hooks that EDR installs.

Walkthrough

A minimal RWX loader pattern (detected by modern EDR):

void* m = VirtualAlloc(0,len,0x3000,0x40); memcpy(m,buf,len); ((void(*)())m)();
C

Hunt for suspicious memory access via Sysmon Event 10:

Get-WinEvent -FilterHashtable @{LogName='...Sysmon/Operational';Id=10} -MaxEvents 50
PowerShell

Detection and Defense

Detect RWX allocations, unbacked executable memory, and abnormal syscall stubs with modern EDR.

Enable ACG/CIG and monitor for sleep-mask behavior.

Conclusion

Loaders evade by minimizing artifacts; memory-integrity telemetry catches what signatures miss.

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