Windows PowerShell SSH Remoting Stub

win_powershell_ssh.ps1

<#
.SYNOPSIS
Windows PowerShell SSH Server Subsystem Shim.

.DESCRIPTION
Used as a basic wrapper for Windows PowerShell that allows it to be used as a target for SSH based remoting sessions.
This allows a PowerShell client to target a Windows host through SSH without having PowerShell 7 installed.

.NOTES
This is experimental and used as a POC.
It is not guaranteed to be stable or bug free.
See https://gist.github.com/jborean93/7d4cb107fa06251b080fa10ec844893e?permalink_comment_id=4093819#gistcomment-4093819 for more info.
#>
[CmdletBinding()]
param ()

$ErrorActionPreference = 'Stop'

Add-Type -Namespace PSSSH -Name NativeMethods -MemberDefinition @'
[DllImport("Kernel32.dll", EntryPoint = "GetStdHandle", SetLastError = true)]
private static extern IntPtr GetStdHandleNative(
    int nStdHandle);

public static Microsoft.Win32.SafeHandles.SafeFileHandle GetStdHandle(int handleId)
{
    IntPtr handle = GetStdHandleNative(handleId);
    if (handle == (IntPtr)(-1)) {
        throw new System.ComponentModel.Win32Exception();
    }

    // Std handles should not be freed.
    return new Microsoft.Win32.SafeHandles.SafeFileHandle(handle, false);
}
'@
# Cannot use [System.Console]::OpenStandardInput() as it's a ConsoleStream and
# will be unable to read input from an SSH based process.
# https://github.com/PowerShell/PowerShell/issues/14478#issuecomment-1064764004
$stdin = [PSSSH.NativeMethods]::GetStdHandle(-10)
$stdinFS = New-Object System.IO.FileStream $stdin, "Read"

$version = $PSVersionTable.PSVersion
$proc = New-Object System.Diagnostics.Process
$proc.StartInfo.FileName = "C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe"
$proc.StartInfo.Arguments = "-Version $($version.Major).$($version.Minor) -NoLogo -ServerMode"
$proc.StartInfo.CreateNoWindow = $true
$proc.StartInfo.RedirectStandardInput = $true
$proc.StartInfo.UseShellExecute = $false
$null = $proc.Start()

$utf8 = New-Object System.Text.UTF8Encoding $false
$stdinSR = New-Object System.IO.StreamReader $stdinFS, $utf8
while ($true) {
    $line = $stdinSR.ReadLine()
    $proc.StandardInput.WriteLine($line)
    $proc.StandardInput.Flush()

    # Sent by the server to indicate the Runspace Pool is closed.
    if ($line.StartsWith("<CloseAck PSGuid='00000000-0000-0000-0000-000000000000' />")) {
        break
    }
}

$proc | Stop-Process -Force

This is absolute gold.

I was pulling my hairs out trying to get PS7 -> PS5.1 working over SSH. Your script seems to work beautifully.

You deserve a cookie, my man.