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ATT&CK Technique

Compile After Delivery

T1027.004 · stealth

Adversaries may attempt to make payloads difficult to discover and analyze by delivering files to victims as uncompiled code. Text-based source code files may subvert analysis and scrutiny from protections targeting executables/binaries. These payloads will need to be compiled before execution.

typically via native utilities such as ilasm.exe, csc.exe, or GCC/MinGW. Source code payloads may also be encrypted, encoded, and/or embedded within other files, such as those delivered as a Phishing. Payloads may also be delivered in formats unrecognizable and inherently benign to the native OS (ex: EXEs on macOS/Linux) before later being (re)compiled into a proper executable binary with a bundled compiler and execution framework.

LinuxmacOSWindows
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Actors Using This

1
north_koreaContagious Interview
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Atomic Tests

5
Executable Atomic Red Team test cases for exercising this technique in a lab. Copy a command, run it on the listed platform, confirm your detections fire.
command_promptwindowsCompile After Delivery using csc.exe
Compile C# code using csc.exe binary used by .NET Upon execution an exe named T1027.004.exe will be placed in the temp folder 
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe /out:#{output_file} "#{input_file}"
powershellwindowsDynamic C# Compile
When C# is compiled dynamically, a .cmdline file will be created as a part of the process. Certain processes are not typically observed compiling C# code, but can do so without touching disk. This can be used to unpack a payload for execution. The exe file that will be executed is named as T1027.004_DynamicCompile.exe is contained in the 'bin' folder of this atomic, and the source code to the file is in the 'src' folder. Upon execution, the exe will print 'T1027.004 Dynamic Compile'. 
Invoke-Expression "#{input_file}"
shlinux, macosC compile
Compile a c file with either gcc or clang on FreeBSD, Linux or Macos. 
gcc #{input_file} && ./a.out
clang #{input_file} && ./a.out
shlinux, macosCC compile
Compile a c file with either gcc or clang on FreeBSD, Linux or Macos. 
g++ #{input_file} && ./a.out
clang++ #{input_file} && ./a.out
shlinux, macosGo compile
Compile a go file with golang on FreeBSD, Linux or Macos. 
go run #{input_file}
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Detection Coverage

1/6 layers
Coverage across standard detection surfaces. Rows marked none have no rule of that type mapped. Some are real blind spots worth closing; others are simply not applicable to this technique (e.g. YARA matches malware files, not network behaviour).
Behavioral / log (Sigma) 5
Analytics (MITRE CAR) none
Runtime / container (Falco) none
File / malware (YARA) none
Network (Suricata/Snort) none
Vuln scan (Nuclei) none
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