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Fix the shadowing command bypass via alias for Import/Export-PSSession #28217

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Aditya Patwardhan (adityapatwardhan) wants to merge 1 commit into from
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Fix the shadowing command bypass via alias for Import/Export-PSSession #28217

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13 changes: 10 additions & 3 deletions src/Microsoft.PowerShell.Commands.Utility/commands/utility/ImplicitRemotingCommands.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1419,18 +1419,25 @@ private void AddRemoteCommandMetadata(
return;
}

if (resolvedCommandName != null && !IsSafeNameOrIdentifier(commandMetadata.Name))
if (resolvedCommandName is not null && !IsSafeNameOrIdentifier(resolvedCommandName))
{
this.WriteError(this.GetErrorSkippedUnsafeCommandName(resolvedCommandName));
return;
}

if (IsCommandSkippedByServerDeclaration(commandMetadata.Name))
// - We do the skip-list check on 'commandMetadata.Name' regardless to keep the existing behavior.
// - We do the skip-list check on the resolved command if no prefix is specified, to avoid a server skipped command
// from being exported and shadow the same-name command on client side without the user explicitly asking for it.
if (IsCommandSkippedByServerDeclaration(commandMetadata.Name)
|| (resolvedCommandName is not null
&& string.IsNullOrEmpty(Prefix)
&& IsCommandSkippedByServerDeclaration(resolvedCommandName)))
{
return;
}

if (!IsCommandNameAllowedForImport(commandMetadata.Name))
if (!IsCommandNameAllowedForImport(commandMetadata.Name)
|| (resolvedCommandName is not null && !IsCommandNameAllowedForImport(resolvedCommandName)))
{
return;
}
Expand Down
61 changes: 60 additions & 1 deletion test/powershell/Modules/Microsoft.PowerShell.Utility/Implicit.Remoting.Tests.ps1
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Original file line number Diff line number Diff line change
Expand Up @@ -1823,7 +1823,11 @@ try

It "Bad verb alias causes no error or warning" {
try {
$ps = [powershell]::Create().AddCommand("Import-PSSession", $true).AddParameter("Session", $session).AddParameter("CommandName", "BadVerb-Variable")
$ps = [powershell]::Create().
AddCommand("Import-PSSession", $true).
AddParameter("Session", $session).
AddParameter("CommandName", "BadVerb-Variable").
AddParameter("AllowClobber")
$module = $ps.Invoke() | Select-Object -First 1

$ps.Streams.Error.Count | Should -Be 0
Expand Down Expand Up @@ -2077,6 +2081,61 @@ try
$errorVariable | Should -BeNullOrEmpty
}
}

Describe "Import-PSSession resolved command of an alias" -tags "Feature","RequireAdminOnWindows" {

BeforeAll {
if ($skipTest) { return }
$session = New-RemoteSession

# Define a remote function
Invoke-Command -Session $session { function MyFunction { "Remote!" } Set-Alias SafeAlias -Value MyFunction }
# Define an alias to 'Get-Help', which is in the skip-list of the remote session configuration.
Invoke-Command -Session $session { Set-Alias -Name myhelp -Value Get-Help }
}

AfterAll {
if ($skipTest) { return }
if ($null -ne $session) { Remove-PSSession $session -ErrorAction SilentlyContinue }
}

It "When '-AllowClobber' is false, shadowing command cannot be bypassed using an alias to it" -Skip:$skipTest {
function MyFunction { "Local!" }

{ Import-PSSession -Session $session -CommandName SafeAlias -AllowClobber:$false -DisableNameChecking } | Should -Throw -ErrorId "ErrorNoCommandsImportedBecauseOfSkipping,Microsoft.PowerShell.Commands.ImportPSSessionCommand"
MyFunction | Should -BeExactly "Local!"
}

It "Command in server skip-list cannot be bypassed using an alias to it" -Skip:$skipTest {
try {
$m = Import-PSSession -Session $session -CommandName myhelp -AllowClobber
$m.ExportedCommands.Count | Should -Be 0
{ myhelp } | Should -Throw -ErrorId "CommandNotFoundException"
}
finally {
if ($null -ne $m) {
Remove-Module $m -Force -ErrorAction SilentlyContinue
Remove-Item $m.ModuleBase -Recurse -Force -ErrorAction SilentlyContinue
}
}
}

It "Server skip-list check should be skipped for the resolved command of an alias when '-Prefix' is specified" -Skip:$skipTest {
try {
$m = Import-PSSession -Session $session -CommandName myhelp -AllowClobber -Prefix "Remote"
$m.ExportedCommands.Count | Should -Be 2
$exportedCommands = Get-Command -Module $m -All | ForEach-Object Name
$exportedCommands | Should -Contain "Remotemyhelp"
$exportedCommands | Should -Contain "Get-RemoteHelp"
}
finally {
if ($null -ne $m) {
Remove-Module $m -Force -ErrorAction SilentlyContinue
Remove-Item $m.ModuleBase -Recurse -Force -ErrorAction SilentlyContinue
}
}
}
}
}
finally
{
Expand Down
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