.. /Microsoft.Workflow.Compiler.exe
Star

A utility included with .NET that is capable of compiling and executing C# or VB.net code.

Paths:

C:\Windows\Microsoft.Net\Framework64\v4.0.30319\Microsoft.Workflow.Compiler.exe

Resources:

Acknowledgements:

Matt Graeber (@mattifestation)
John Bergbom (@BergbomJohn)
FortyNorth Security (@FortyNorthSec)
Bank Security (@Bank_Security)

Detection:

Sigma: https://github.com/SigmaHQ/sigma/blob/c04bef2fbbe8beff6c7620d5d7ea6872dbe7acba/rules/windows/process_creation/proc_creation_win_lolbin_workflow_compiler.yml
Splunk: https://github.com/splunk/security_content/blob/961a81d4a5cb5c5febec4894d6d812497171a85c/detections/endpoint/suspicious_microsoft_workflow_compiler_usage.yml
Splunk: https://github.com/splunk/security_content/blob/18f63553a9dc1a34122fa123deae2b2f9b9ea391/detections/endpoint/suspicious_microsoft_workflow_compiler_rename.yml
Elastic: https://github.com/elastic/detection-rules/blob/414d32027632a49fb239abb8fbbb55d3fa8dd861/rules/windows/defense_evasion_unusual_process_network_connection.toml
Elastic: https://github.com/elastic/detection-rules/blob/414d32027632a49fb239abb8fbbb55d3fa8dd861/rules/windows/defense_evasion_network_connection_from_windows_binary.toml
BlockRule: https://docs.microsoft.com/en-us/windows/security/threat-protection/windows-defender-application-control/microsoft-recommended-block-rules
IOC: Microsoft.Workflow.Compiler.exe would not normally be run on workstations.
IOC: The presence of csc.exe or vbc.exe as child processes of Microsoft.Workflow.Compiler.exe
IOC: Presence of "<CompilerInput" in a text file.

Execute

Compile and execute C# or VB.net code in a XOML file referenced in the test.xml file.
```
Microsoft.Workflow.Compiler.exe tests.xml results.xml
```
Use case
Compile and run code

Privileges required
User

Operating systems
Windows 10S, Windows 11

ATT&CK® technique
T1127
Compile and execute C# or VB.net code in a XOML file referenced in the test.txt file.
```
Microsoft.Workflow.Compiler.exe tests.txt results.txt
```
Use case
Compile and run code

Privileges required
User

Operating systems
Windows 10S, Windows 11

ATT&CK® technique
T1127

AWL bypass

Compile and execute C# or VB.net code in a XOML file referenced in the test.txt file.
```
Microsoft.Workflow.Compiler.exe tests.txt results.txt
```
Use case
Compile and run code

Privileges required
User

Operating systems
Windows 10S, Windows 11

ATT&CK® technique
T1127