A utility included with .NET that is capable of compiling and executing C# or VB.net code.
Microsoft.Workflow.Compiler.exe tests.xml results.xml
Compile and execute C# or VB.net code in a XOML file referenced in the test.xml file.
Compile and run code
C:\Windows\Microsoft.Net\Framework64\v4.0.30319\Microsoft.Workflow.Compiler.exe
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.
Matt Graeber (@mattifestation), John Bergbom (@BergbomJohn), FortyNorth Security (@FortyNorthSec), Bank Security (@Bank_Security)