Windows Authentication not working on local IIS 7.5. Error 401.1

Question

I recently had a nasty issue getting Windows Authentication to work on a local instance of IIS 7.5 (Windows 7 Pro) to an ASP.net 4.0 site. I followed the basic steps.

IIS Authentication

• Disable Anonymous Authentication
• Enable Windows Authentication

Edit web.config

<authentication mode="Windows" />

This did a nice job of enabling Windows Authentication but every attempt to login was rejected and ultimately returned a 401.1 error. This is where the problem started. There appear to be many reasons for this that are well documented around the web including here on Stack Overflow.

I'd tried:

• Editing IIS Authentication 'Advanced settings' for Windows Authentication to disable Extended Protection and Kernel-mode authentication
• Editing IIS Authentication 'Providers' to move NTLM above Negotiate.
• Editing IIS .NET Authorization Rules to explicity Allow users (and various other combinations).
• Various IIS command line scripts and tweaks.
• Various config tweaks in web.config file.
• Even some file system permissions tweaks.

But all to no avail, the dreaded 401.1 remained.

This really is a case of "can't see the wood for the trees". None of the solutions I managed to find (call it a case of bad search parameters if you will) worked for me so I thought it worth posting this question to, hopefully, provide a clear answer that's easier to find for anyone suffering the same issue.

Answer 1

The issue here is that modern versions of Windows (Windows XP SP2, Windows Server 2003 SP1 and up) include a loopback check security feature that is designed to help prevent reflection attacks on your computer. Therefore, authentication fails if the FQDN or the custom host header that you use does not match the local computer name.

This can be resolved by either explicitly specifying host names or by disabling the loopback check. Obviously the former being the more controlled approach.

1. Set the DisableStrictNameChecking registry entry to 1. See: 281308 (Note: This should be unnecessary for Windows Server 2008/Vista and later)
2. In Registry Editor, locate and then click the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0
3. Right-click MSV1_0, point to New, and then click Multi-String Value.
4. Type BackConnectionHostNames, and then press ENTER.
5. Right-click BackConnectionHostNames, and then click Modify.
6. In the Value data box, type the host name or the host names for the sites that are on the local computer, and then click OK.
7. Quit Registry Editor, and then restart the IISAdmin service.

Full details of how do to this can be found on MSDN: 896861

Hope this helps someone out. If you have any alternate suggestions or improvements please add.

Answer 2

I want to add Michael Dark's comment as an answer because I don't have permissions to modify my registry so Pete's answer doesn't work for me but I was able to solve the problem.

I solved it by adding a new Binding to my website with no specified host name and a different port (because localhost:80 is used for me). As soon as I tried calling it from http://localhost:86/mypage, it worked. After a quick check in the browser, I tested a few times with cURL and it correctly accepted and rejected my credentials.

Answer 3

Reinstall your IIS features again and make sure that WINDOWS auth checkbox statys checked.

Answer 4

Here's the PowerShell code that I use to deal with back connection host names and IIS. Note that with a little work, the commandlets can be saved out to a module and used that way.

Import-Module WebAdministration

function Add-BackConnectionHostname
{
    <#
    .SYNOPSIS
    Adds the back connection hostnames that will bypass the server loopback check.
    .DESCRIPTION
    Adds the hostname to the list of back connection hostnames that will bypass the server loopback check. Back connection host names  
    can be used to address the problem with IIS sites using Windows Authentication that is described in Microsoft KB896861.
    .EXAMPLE
    Add-BackConnectionHostname mywebsite.mydomain.tld
    .EXAMPLE
    Add-BackConnectionHostname mywebsite1.mydomain.tld, mywebsite2.mydomain.tld
    .PARAMETER Hostname
    The Hostname to add to the back connection hostnames list.
    .LINK
    Remove-BackConnectionHostname
    Get-BackConnectionHostname
    Enable-ServerLoopbackCheck
    Disable-ServerLoopbackCheck
    Get-ServerLoopbackCheck
    "You receive error 401.1 when you browse a Web site that uses Integrated Authentication and is hosted on IIS 5.1 or a later version" (http://support.microsoft.com/en-us/kb/896861)
    #>
    [CmdletBinding(SupportsShouldProcess = $true)]
    param
    (
        [Parameter(ValueFromPipeline = $true, Mandatory = $true)]
        [string] $Hostname
    )

    begin
    {
        $keyPath = "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0"
        $propertyName = "BackConnectionHostnames"
        $key = Get-Item $keyPath
        $property = $null
        $propertyValues = $null

        if ($key -ne $null)
        {
            $property = Get-ItemProperty $keyPath -Name $propertyName -ErrorAction SilentlyContinue

            if ($property -eq $null)
            {
                $property = New-ItemProperty $keyPath -Name $propertyName -Value $null -PropertyType ([Microsoft.Win32.RegistryValueKind]::MultiString) -ErrorAction Stop

                Write-Verbose "Created the $($propertyName) property."
            }

            if ($property -ne $null)
            {
                $propertyValues = $property.$propertyName
            }
        }
    }

    process
    {
        if ($property -ne $null)
        {
            foreach ($hostNameValue in $Hostname)
            {
                if ([string]::IsNullOrWhiteSpace($hostName) -eq $false -and $propertyValues -notcontains $hostNameValue)
                {
                    $propertyValues += $hostNameValue

                    Write-Verbose "Added $($hostName) to the back connection hostnames."
                }
                else
                {
                    Write-Verbose "Back connection host names already has an entry for $($hostName)."
                }
            }
        }
    }

    end
    {
        if ($propertyValues -ne $null)
        {
            $propertyValues = $propertyValues | ?{ [string]::IsNullOrWhiteSpace($_) -eq $false } | Sort -Unique
            Set-ItemProperty $keyPath -Name $propertyName -Value $propertyValues
        }
    }
}

function Remove-BackConnectionHostname
{
    <#
    .SYNOPSIS
    Removes the hostname from the list of back connection hostnames that will bypass the server loopback check.
    .DESCRIPTION
    Removes the hostname from the list of back connection hostnames that will bypass the server loopback check.
    .EXAMPLE
    Remove-BackConnectionHostname mywebsite.mydomain.tld
    .EXAMPLE
    Remove-BackConnectionHostname mywebsite1.mydomain.tld, mywebsite2.mydomain.tld
    .PARAMETER Hostname
    The Hostname to remove from the back connection hostnames list.
    .LINK
    Add-BackConnectionHostname
    Get-BackConnectionHostname
    Enable-ServerLoopbackCheck
    Disable-ServerLoopbackCheck
    Get-ServerLoopbackCheck
    "You receive error 401.1 when you browse a Web site that uses Integrated Authentication and is hosted on IIS 5.1 or a later version" (http://support.microsoft.com/en-us/kb/896861)
    #>
    [CmdletBinding(SupportsShouldProcess = $true)]
    param
    (
        [Parameter(ValueFromPipeline = $true, Mandatory = $true)]
        [string] $Hostname
    )

    begin
    {
        $keyPath = "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0"
        $propertyName = "BackConnectionHostnames"
        $key = Get-Item $keyPath
        $property = $null
        $propertyValues = $null

        if ($key -ne $null)
        {
            $property = Get-ItemProperty $keyPath -Name $propertyName -ErrorAction SilentlyContinue

            if ($property -ne $null)
            {
                $propertyValues = $property.$propertyName
            }
            else
            {
                Write-Verbose "The $($propertyName) property was not found."
            }
        }
    }

    process
    {
        if ($property -ne $null)
        {
            foreach ($hostNameValue in $Hostname)
            {
                if ($propertyValues -contains $hostNameValue)
                {
                    $propertyValues = $propertyValues | ? { $_ -ne $hostName }

                    Write-Verbose "Removed $($hostName) from the $($propertyName) property."
                }
                else
                {
                    Write-Verbose "No entry for $($hostName) was found in the $($propertyName) property."
                }
            }
        }
    }

    end
    {
        if ($property -ne $null)
        {
            $propertyValues = $propertyValues | ?{ [string]::IsNullOrWhiteSpace($_) -eq $false } | Sort -Unique

            if ($propertyValues.Length -ne 0)
            {
                Set-ItemProperty $keyPath -Name $propertyName -Value $propertyValues
            }
            else
            {
                Remove-ItemProperty $keyPath -Name $propertyName

                Write-Verbose "No entries remain after removing $($hostName). The $($propertyName) property was removed."
            }
        }
    }
}

function Get-BackConnectionHostname
{
    <#
    .SYNOPSIS
    Gets the list of back connection hostnames that will bypass the server loopback check.
    .DESCRIPTION
    Gets the back connection hostnames that will bypass the server loopback check. Back connection host names can be used to address 
    the problem with IIS sites using Windows Authentication that is described in Microsoft KB896861.
    .EXAMPLE
    Get-BackConnectionHostname
    .LINK
    Add-BackConnectionHostname
    Remove-BackConnectionHostname
    Enable-ServerLoopbackCheck
    Disable-ServerLoopbackCheck
    Get-ServerLoopbackCheck
    "You receive error 401.1 when you browse a Web site that uses Integrated Authentication and is hosted on IIS 5.1 or a later version" (http://support.microsoft.com/en-us/kb/896861)
    #>
    [CmdletBinding(SupportsShouldProcess = $false)]
    param
    (
    )

    begin
    {
        $keyPath = "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0"
        $propertyName = "BackConnectionHostnames"
        $key = Get-Item $keyPath
        $property = $null

        if ($key -ne $null)
        {
            $property = Get-ItemProperty $keyPath -Name $propertyName -ErrorAction SilentlyContinue

            if ($property -eq $null)
            {
                Write-Verbose "The $($propertyName) property was not found."
            }
        }
    }

    process
    {
        $propertyValues = $null

        if ($property -ne $null)
        {
            $propertyValues = $property.$propertyName
        }

        return $propertyValues
    }

    end
    {
    }
}

function Enable-ServerLoopbackCheck
{
    <#
    .SYNOPSIS
    Enables the server loopback check. Enabled is the normal state for a Windows Server.
    .DESCRIPTION
    Enables the server loopback check. Having the loopback check enabled is the normal state for a Windows Server. Disabling the loopback check can be used to address 
    the problem with IIS sites using Windows Authentication that is described in Microsoft KB896861. It is NOT the preferred method. See the KB article for more details.
    .EXAMPLE
    Enable-ServerLoopbackCheck
    .LINK
    Add-BackConnectionHostname
    Remove-BackConnectionHostname
    Get-BackConnectionHostname
    Enable-ServerLoopbackCheck
    Get-ServerLoopbackCheck
    "You receive error 401.1 when you browse a Web site that uses Integrated Authentication and is hosted on IIS 5.1 or a later version" (http://support.microsoft.com/en-us/kb/896861)
    #>
    [CmdletBinding(SupportsShouldProcess = $true)]
    param
    (
    )

    begin
    {
        $keyPath = "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa"
        $propertyName = "DisableLoopbackCheck"
        $key = Get-Item $keyPath
        $property = $null

        if ($key -ne $null)
        {
            $property = Get-ItemProperty $keyPath -Name $propertyName -ErrorAction SilentlyContinue

            if ($property -eq $null)
            {
                Write-Verbose "The $($propertyName) property was not found."
            }
        }
    }

    process
    {
        if ($property -ne $null)
        {
            Set-ItemProperty $keyPath -Name $propertyName -Value 0
        }
    }

    end
    {
    }
}

function Disable-ServerLoopbackCheck
{
    <#
    .SYNOPSIS
    Disables the server loopback check for all hostnames. Enabled is the normal state for a Windows Server.
    .DESCRIPTION
    Disables the server loopback check for all hostnames. Having the loopback check enabled is the normal state for a Windows Server. Disabling the loopback check can be used 
    to address the problem with IIS sites using Windows Authentication that is described in Microsoft KB896861. It is NOT the preferred method. See the KB article for more details.
    .EXAMPLE
    Disable-ServerLoopbackCheck
    .LINK
    Add-BackConnectionHostname
    Remove-BackConnectionHostname
    Get-BackConnectionHostname
    Enable-ServerLoopbackCheck
    Get-ServerLoopbackCheck
    "You receive error 401.1 when you browse a Web site that uses Integrated Authentication and is hosted on IIS 5.1 or a later version" (http://support.microsoft.com/en-us/kb/896861)
    #>
    [CmdletBinding(SupportsShouldProcess = $true)]
    param
    (
    )

    begin
    {
        $keyPath = "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa"
        $propertyName = "DisableLoopbackCheck"
        $key = Get-Item $keyPath
        $property = $null

        if ($key -ne $null)
        {
            $property = Get-ItemProperty $keyPath -Name $propertyName -ErrorAction SilentlyContinue

            if ($property -eq $null)
            {
                Write-Verbose "The $($propertyName) property was not found."
            }
        }
    }

    process
    {
        if ($property -ne $null)
        {
            Set-ItemProperty $keyPath -Name $propertyName -Value 1
        }
        else
        {
            $property = New-ItemProperty $keyPath -Name $propertyName -PropertyType ([Microsoft.Win32.RegistryValueKind]::DWord) -Value 1
        }
    }

    end
    {
    }
}

function Get-ServerLoopbackCheck
{
    <#
    .SYNOPSIS
    Gets the status of the server loopback check. Enabled is the normal state for a Windows Server.
    .DESCRIPTION
    Gets the status of the server loopback check. Having the loopback check enabled is the normal state for a Windows Server. Disabling the loopback check can be used 
    to address the problem with IIS sites using Windows Authentication that is described in Microsoft KB896861. It is NOT the preferred method. See the KB article for 
    more details.
    .EXAMPLE
    Get-ServerLoopbackCheck
    .LINK
    Add-BackConnectionHostname
    Remove-BackConnectionHostname
    Get-BackConnectionHostname
    Enable-ServerLoopbackCheck
    Disable-ServerLoopbackCheck
    "You receive error 401.1 when you browse a Web site that uses Integrated Authentication and is hosted on IIS 5.1 or a later version" (http://support.microsoft.com/en-us/kb/896861)
    #>
    [CmdletBinding(SupportsShouldProcess = $false)]
    param
    (
    )

    begin
    {
        $keyPath = "HKLM:\SYSTEM\CurrentControlSet\Control\Lsa"
        $propertyName = "DisableLoopbackCheck"
        $key = Get-Item $keyPath
        $property = $null

        if ($key -ne $null)
        {
            $property = Get-ItemProperty $keyPath -Name $propertyName -ErrorAction SilentlyContinue
        }
    }

    process
    {
        $loopbackCheckStatus = "Enabled"

        if ($property -ne $null)
        {
            switch ($property)
            {
                0 { $loopbackCheckStatus = "Enabled" }
                1 { $loopbackCheckStatus = "Disabled" }
                default { $loopbackCheckStatus = "Unknown" }
            }
        }

        return $loopbackCheckStatus
    }

    end
    {
    }
}

function Get-WebsiteHostname
{
    <#
    .SYNOPSIS
    Gets the hostnames for the IP addresses bound to a web site.
    .DESCRIPTION
    Gets the hostnames for the IP addresses bound to a web site. Where a host header exists, the host header is used; otherwise, the IP address is looked up
    in DNS to see if a PTR record exists.
    .EXAMPLE
    Get-WebSiteHostname $webSite
    .EXAMPLE
    Get-WebSiteHostname -Name 'Default Web Site'
    .EXAMPLE
    Get-Website | Get-WebSiteHostname
    .LINK
    Get-Website 
    #>
    [CmdletBinding(SupportsShouldProcess = $false)]
    param
    (
        [Parameter(ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true, Mandatory = $true)]
        [string] $Name
    )

    process
    {
        $siteHostnames = @()

        foreach ($webSiteName in $Name)
        {
            $bindings = Get-WebBinding -Name $Name

            foreach ($binding in $bindings)
            {
                $bindingInfo = $binding.bindingInformation.Split(':')
                $hostHeader = $bindingInfo[2]
                $bindingInfoAddress = $null
                $isValidIP = [System.Net.IPAddress]::TryParse($bindingInfo[0], [ref] $bindingInfoAddress)
                $siteHostname = $null

                if ($bindingInfo -eq '*')
                {
                    Write-Warning "The $($webSiteName) web site has a binding address set to All Unassigned."
                }
                elseif ([string]::IsNullOrWhiteSpace($hostHeader) -eq $false)
                {
                    $siteHostname = $hostHeader
                    Write-Verbose "The $($webSiteName) web site has a host header set to $($siteHostname)."
                }
                elseif ($isValidIP -eq $true)
                {
                    $siteHostname = (Resolve-DnsName $bindingInfoAddress -DnsOnly PTR -ErrorAction SilentlyContinue).NameHost

                    if ($siteHostname -ne $null)
                    {
                        Write-Verbose "The $($webSiteName) web site has an IP Address $($bindingInfoAddress) that resolves to $($siteHostname)."
                    }
                    else
                    {
                        Write-Warning "The $($webSiteName) web site has an IP Address $($bindingInfoAddress) with no PTR record."
                    }
                }
            }

            if ($siteHostname -ne $null)
            {
                $siteHostnames += $siteHostname
            }
        }

        return $siteHostnames | Sort -Unique
    }
}

Get-Website | ?{ (Get-WebConfiguration -Filter '/system.web/authentication' -PSPath $_.PSPath).mode -eq 'Windows' } | Get-WebsiteHostname | Add-BackConnectionHostname