Silent Execution Of cmd.exe With Redirected STDERR And STDOUT

The ability to execute commands silently using cmd.exe while redirecting both standard output (STDOUT) and standard error (STDERR) is a common technique employed in both legitimate administrative tasks and malicious activities.

This method ensures that the command execution remains hidden from the user, while capturing or discarding the output for further processing.

Key Techniques

1. Silent Execution with /Q and /C:

• The /Q switch turns off echo, ensuring that commands do not display their execution.
• The /C switch executes the specified command and then terminates the command processor.
• Example: cmd.exe /Q /C "command"

1. Output Redirection:

• By default, cmd.exe separates outputs into two streams:
  • STDOUT (stream 1): Regular output.
  • STDERR (stream 2): Error messages.
• To redirect both streams to the same location, use 2>&1. This redirects STDERR to STDOUT, which can then be redirected to a file, a pipe, or discarded.
• Example: command > output.log 2>&1

1. Common Redirection Scenarios:

• Redirecting all output to a file: command > alloutput.log 2>&1
• Discarding all output: command > nul 2>&1

Several open-source tools and frameworks leverage silent execution with redirection for stealthy operations:

• Impacket: Often used for remote command execution, Impacket employs cmd.exe /Q /C along with redirection for capturing outputs remotely.
• CrackMapExec and NetExec: These tools use similar techniques for lateral movement and remote command execution in penetration testing or malicious activities.

Identifying silent cmd.exe executions with redirected outputs is crucial in detecting potential malicious activities. Key indicators include:

• Command-line arguments containing /Q, /C, and redirection operators (>, 2>&1).
• Event logs (e.g., Windows Event ID 4688) showing suspicious cmd.exe invocations.
• Parent-child process relationships where cmd.exe is spawned by unusual processes like wmiprvse.exe.

Example query for detection using Microsoft Defender for Endpoint:

DeviceProcessEvents
| where FileName =~ "cmd.exe"
| where ProcessCommandLine has_all ("/Q", "/C")
| where ProcessCommandLine has_any ("&1", "2>&1")

Silent execution of cmd.exe with redirected STDERR and STDOUT is a powerful technique for both legitimate automation and adversarial tactics.

While it enables efficient command execution without user interaction, its misuse necessitates vigilant monitoring through process auditing, event logging, and advanced threat-hunting queries.