• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Windows Security change affecting PowerShell


The recent (1/8/2019) Windows security patch CVE-2019-0543, has introduced a breaking change for a PowerShell remoting scenario. It is a narrowly scoped scenario that should have low impact for most users.

The breaking change only affects local loopback remoting, which is a PowerShell remote connection made back to the same machine, while using non-Administrator credentials.

PowerShell remoting endpoints do not allow access to non-Administrator accounts by default. However, it is possible to modify endpoint configurations, or create new custom endpoint configurations, that do allow non-Administrator account access. So you would not be affected by this change, unless you explicitly set up loopback endpoints on your machine to allow non-Administrator account access.

Example of broken loopback scenario

# Create endpoint that allows Users group access
PS > Register-PSSessionConfiguration -Name MyNonAdmin -SecurityDescriptorSddl 'O:NSG:BAD:P(A;;GA;;;BA)(A;;GA;;;BU)S:P(AU;FA;GA;;;WD)(AU;SA;GXGW;;;WD)' -Force

# Create non-Admin credential
PS > $nonAdminCred = Get-Credential ~\NonAdminUser

# Create a loopback remote session to custom endpoint using non-Admin credential
PS > $session = New-PSSession -ComputerName localhost -ConfigurationName MyNonAdmin -Credential $nonAdminCred

New-PSSession : [localhost] Connecting to remote server localhost failed with the following error message : The WSMan
service could not launch a host process to process the given request.  Make sure the WSMan provider host server and
proxy are properly registered. For more information, see the about_Remote_Troubleshooting Help topic.
At line:1 char:1
+ New-PSSession -ComputerName localhost -ConfigurationName MyNonAdmin - ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : OpenError: (System.Manageme....RemoteRunspace:RemoteRunspace) [New-PSSession], PSRemotin
    + FullyQualifiedErrorId : -2146959355,PSSessionOpenFailed

The above example fails only when using non-Administrator credentials, and the connection is made back to the same machine (localhost). Administrator credentials still work. And the above scenario will work when remoting off-box to another machine.

Example of working loopback scenario

# Create Admin credential
PS > $adminCred = Get-Credential ~\AdminUser

# Create a loopback remote session to custom endpoint using Admin credential
PS > $session = New-PSSession -ComputerName localhost -ConfigurationName MyNonAdmin -Credential $adminCred
PS > $session

 Id Name            ComputerName    ComputerType    State         ConfigurationName     Availability
 -- ----            ------------    ------------    -----         -----------------     ------------
  1 WinRM1          localhost       RemoteMachine   Opened        MyNonAdmin               Available

The above example uses Administrator credentials to the same MyNonAdmin custom endpoint, and the connection is made back to the same machine (localhost). The session is created successfully using Administrator credentials.

The breaking change is not in PowerShell but in a system security fix that restricts process creation between Windows sessions. This fix is preventing WinRM (which PowerShell uses as a remoting transport and host) from successfully creating the remote session host, for this particular scenario. There are no plans to update WinRM.

This affects Windows PowerShell and PowerShell Core 6 (PSCore6) WinRM based remoting.

This does not affect SSH remoting with PSCore6.

This does not affect JEA (Just Enough Administration) sessions.

A workaround for a loopback connection is to always use Administrator credentials.

Another option is to use PSCore6 with SSH remoting.

Paul Higinbotham
Senior Software Engineer
PowerShell Team

Source: Windows Security change affecting PowerShell | PowerShell Team Blog

My Computer

System One

  • OS
    64-bit Windows 10
    Computer type
    System Manufacturer/Model Number
    Custom self built
    Intel i7-8700K OC'd to 5 GHz
    ASUS ROG Maximus XI Formula Z390
    16 GB (8GBx2) G.SKILL TridentZ DDR4 3200 MHz
    Graphics Card(s)
    Sound Card
    Integrated Digital Audio (S/PDIF)
    Monitor(s) Displays
    3 x 27" Asus VE278Q
    Screen Resolution
    Hard Drives
    250GB Samsung 960 EVO M.2,
    256GB OCZ Vector,
    6TB WD Black WD6001FZWX
    8TB WD MyCloudEX2Ultra NAS
    OCZ Series Gold OCZZ1000M 1000W
    Thermaltake Core P3
    Corsair Hydro H115i
    Logitech wireless K800
    Logitech MX Master
    Internet Speed
    1 Gb/s Download and 35 Mb/s Upload
    Internet Explorer 11
    Malwarebyte Anti-Malware Premium
    Other Info
    Logitech Z625 speaker system,
    Logitech BRIO 4K Pro webcam,
    HP Color LaserJet Pro MFP M477fdn,
    Linksys EA9500 router,
    Arris SB8200 cable modem,
    Lumia 1520 phone

Users Who Are Viewing This Thread (Users: 0, Guests: 1)