Ssh.exe is the OpenSSH compatible client can be used to connect to Windows 10 (build 1809 and later) and Windows Server 2019 devices.
ssh -o ProxyCommand=calc.exe .
Executes calc.exe from ssh.exe
Performs execution of specified file, can be used as a defensive evasion.
c:\windows\system32\OpenSSH\ssh.exe
Sigma: https://github.com/SigmaHQ/sigma/blob/c04bef2fbbe8beff6c7620d5d7ea6872dbe7acba/rules/windows/process_creation/proc_creation_win_lolbin_ssh.yml, IOC: Event ID 4624 with process name C:\Windows\System32\OpenSSH\sshd.exe., IOC: command line arguments specifying execution.
Akshat Pradhan, Felix Boulet