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Apply implicit-remoting command protections to resolved aliases #28208

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Merged
Justin Chung (jshigetomi) merged 2 commits into from
Oct 16, 2026
Merged

Apply implicit-remoting command protections to resolved aliases #28208

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9a73903
Fix the shadowing command bypass via alias for Import/Export-PSSessio…
daxian-dbw Oct 7, 2026
3579e2d
Merge branch 'master' into 175
jshigetomi Oct 14, 2026
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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))

@iSazonov Ilya (iSazonov) Oct 15, 2026

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Before the change IsSafeNameOrIdentifier was used only once and it threw if null or empty.
Now we always check for not null so we could do the check in IsSafeNameOrIdentifier.

Also here we don't check for empty but do the check below.

Should we move both checks to IsSafeNameOrIdentifier?

{
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;
}
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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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