Regasm.exe

Commands

1. AWL BypassLocal Admin T1218.009

   Execute code and bypass Application whitelisting

   regasm.exe {PATH:.dll}

   Loads the target .NET DLL file and executes the RegisterClass function.

   os: Windows vista, Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11

   Execute: DLL (.NET)

2. ExecuteUser T1218.009

   Execute code and bypass Application whitelisting

   regasm.exe /U {PATH:.dll}

   Loads the target .DLL file and executes the UnRegisterClass function.

   os: Windows vista, Windows 7, Windows 8, Windows 8.1, Windows 10, Windows 11

   Execute: DLL (.NET)

Detection

• Sigma https://github.com/SigmaHQ/sigma/blob/6312dd1d44d309608552105c334948f793e89f48/rules/windows/process_creation/proc_creation_win_lolbin_regasm.yml
• Elastic https://github.com/elastic/detection-rules/blob/12577f7380f324fcee06dab3218582f4a11833e7/rules/windows/execution_register_server_program_connecting_to_the_internet.toml
• Splunk https://github.com/splunk/security_content/blob/bc93e670f5dcb24e96fbe3664d6bcad92df5acad/docs/_stories/suspicious_regsvcs_regasm_activity.md
• Splunk https://github.com/splunk/security_content/blob/bee2a4cefa533f286c546cbe6798a0b5dec3e5ef/detections/endpoint/detect_regasm_with_network_connection.yml
• IOCregasm.exe executing dll file

Resources

• https://pentestlab.blog/2017/05/19/applocker-bypass-regasm-and-regsvcs/
• https://oddvar.moe/2017/12/13/applocker-case-study-how-insecure-is-it-really-part-1/
• https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.009/T1218.009.md