All posts tagged windows firewall

Always On VPN November 2023 Security Updates

Microsoft has released its security updates for November 2023. For Always On VPN administrators, it’s a light month, with just a single CVE affecting Always On VPN infrastructure.

PEAP

CVE-2023-36028 addresses a remote code execution (RCE) vulnerability in the Microsoft Protected Extensible Authentication Protocol (PEAP). An attacker could exploit this vulnerability by sending a specially crafted PEAP packet to a Windows Network Policy Server (NPS). This attack does not require authentication or user interaction.

Affected Systems

This PEAP vulnerability affects only NPS servers configured to support PEAP authentication explicitly. PEAP authentication is a best practice configuration for Always On VPN deployments and is widely deployed. NPS servers deployed to support other services, such as Wi-Fi or router and switch access that are configured to allow PEAP authentication, are also affected.

Exposure

NPS servers are not (or should not be!) exposed directly to the public Internet. This limits the attack surface to adversaries already on the internal network.

Mitigation

Microsoft suggests disabling PEAP authentication support on NPS servers until the update is applied. However, this would break the majority of Always On VPN deployments today. Since disabling PEAP isn’t a viable option, administrators can reduce their attack surface by updating the NPS firewall rules to restrict access only to authorized VPN servers or other network devices until their systems are fully updated.

Additional Information

November 2023 Security Updates

CVE-2023-36028 PEAP Remote Code Execution Vulnerability

4 Comments
by Richard M. Hicks on November 14, 2023  •  Permalink
Posted in Always On VPN, Authentication and MFA, NPS and EAP, Security Updates, Windows Server
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Posted by Richard M. Hicks on November 14, 2023

https://directaccess.richardhicks.com/2023/11/14/always-on-vpn-november-2023-security-updates/

Always On VPN Trusted Network Detection and Native Azure AD Join

Administrators deploying Microsoft Always On VPN are quickly learning that the native Azure Active Directory join (AADJ) model has significant advantages over the more traditional Hybrid Azure AD join (HAADJ) scenario. Native AADJ is much simpler to deploy and manage than HAADJ while still allowing full single sign-on (SSO) to on-premises resources for remote users. Intune even allows for the import of custom ADMX and ADML administrative templates, further reducing the dependency on on-premises Active Directory for device management.

Remote Management

Although devices aren’t joined to the domain, administrators may still wish to access those clients connected to their network for device discovery or to perform administrative tasks. However, when native AADJ clients connect via Always On VPN, the Public Windows firewall profile is assigned to the VPN tunnel adapter. The Public profile is, of course, more restrictive and blocks most management protocols by default.

Firewall Rules

While adding firewall rules to the Public profile to allow management protocols is possible, this isn’t recommended for security reasons. The Public profile is typically loaded when the device is on an untrusted network. Exposing management protocols on an insecure network is asking for trouble.

Domain Profile

Domain-joined or Hybrid AADJ endpoints will use the Domain Windows firewall profile. This profile is more permissive, allowing many standard management protocols by default. Also, administrators can add rules to allow additional access as required without increasing the risk for devices on untrusted networks.

Trusted Network Detection

So, the trick is to get a native AADJ endpoint to load the Domain profile for the VPN tunnel adapter when connected via Always On VPN. Trusted Network Detection is accomplished by using settings configured on the endpoint using the NetworkListManager Configuration Service Provider (CSP).

Intune and XML

There are two settings administrators can enable AADJ devices to detect a trusted network and load the Domain Windows firewall profile. Unfortunately, these settings can only be applied using Intune and the Custom XML template. Administrators will use the following OMA-URI settings.

AllowedTlsAuthenticationEndpoints

The AllowedTlsAuthenticationEndpoints policy setting defines the URL the device uses to validate a trusted network. The target must be an on-premises web server with a valid TLS certificate using HTTPS. The target must be a highly available internal resource inaccessible from the Internet. DirectAccess administrators will be quite familiar with this concept; it’s the Network Location Server (NLS)!

Use the following OMA-URI to configure the TLS authentication endpoint.

URI: ./Device/Vendor/MSFT/Policy/Config/
NetworkListManager/AllowedTlsAuthenticationEndpoints

String: <![CDATA[https://nls.corp.example.net]]>

ConfiguredTlsAuthenticationNetworkName

The ConfiguredTlsAuthenticationNetworkName policy setting is optional. Administrators can use this setting to provide a friendly name for the authenticated trusted network. The FQDN of the target resource (NLS) is used by default. However, using this setting overrides the default with something more meaningful.

Use the following OMA-URI to configure the TLS authentication network name.

URI: ./Device/Vendor/MSFT/Policy/Config/
NetworkListManager/ConfiguredTlsAuthenticationNetworkName

String: <Friendly network name>

Results

Once configured, you’ll find the Always On VPN tunnel adapter uses the Domain Windows firewall profile and an optional friendly network name.

Additional Information

Deploying Always On VPN with Intune using Custom XML and CSP

Always On VPN CSP Updates

Always On VPN and VpnStrategy with CSP

2 Comments
by Richard M. Hicks on June 26, 2023  •  Permalink
Posted in Always On VPN, Authentication and MFA, DirectAccess, Entra ID, Microsoft Intune, PKI, TLS, Windows Server
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Posted by Richard M. Hicks on June 26, 2023

https://directaccess.richardhicks.com/2023/06/26/always-on-vpn-trusted-network-detection-and-native-azure-ad-join/

Always On VPN and Windows Server 2019 NPS Bug

Note: This post updated March 19,2019 to reflect new workaround configuration guidance.

When deploying a Windows Server 2019 Network Policy Server (NPS) to support an Always On VPN implementation, administrators may encounter the following error when attempting to establish a VPN connection on a remote Windows client.

Can’t connect to [connection name].

The connection was prevented because of a policy configured on your RAS/VPN server. Specifically, the authentication method used by the server to verify your username and password may not match the authentication method configured in your connection profile. Please contact the Administrator of the RAS server and notify them of this error.

VPN error stating the connection was prevented because of a policy configured on the RAS/VPN server
In addition, an event ID 20227 from the RasClient will be recorded in the application event log with the following error message.

The user [username] dialed a connection named [connection name] which has failed. The error code returned on failure is 812.

RasClient event 20227 showing the VPN connection failed with error code 812

Common Causes

Always On VPN error code 812 indicates an authentication policy mismatch between the client and the server. This often occurs when, for example, the server is configured to use Protected Extensible Authentication Protocol (PEAP), but the client is configured to use Microsoft CHAP Version 2 (MS-CHAP v2).

Troubleshooting

Carefully review the authentication policy on both the client and server to ensure they match. Next, enable firewall logging on the NPS server to log both allowed and dropped packets. Attempt another VPN connection and observe the firewall logs. In this example the firewall is dropping packets inbound on UDP port 1812.

Windows Firewall log on the NPS server showing dropped inbound UDP 1812 packets

Interestingly, the default Windows firewall rule allowing inbound UDP port 1812 is enabled and set to allow for all profiles.

Default Windows Firewall rule for inbound RADIUS authentication on UDP 1812 enabled for all profiles

Windows Server 2019 Bug

It appears that Microsoft’s recently released Windows Server 2019 has a bug that prevents NPS from working correctly out of the box. Specifically, it looks like the default Windows firewall rules to allow inbound UDP port 1812 (RADIUS authentication) and inbound UDP port 1813 (RADIUS accounting) do not work.

Resolution

To resolve this issue, open an elevated command window and enter the following command.

sc.exe sidtype IAS unrestricted

Once complete, restart the server and the default Windows Firewall rules for NPS traffic will work correctly.

Additional Information

Always On VPN: Secure Remote Access for Windows

Always On VPN NPS Load Balancing Strategies

32 Comments
by Richard M. Hicks on November 27, 2018  •  Permalink
Posted in Always On VPN, NPS and EAP, PowerShell, Windows Server
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Posted by Richard M. Hicks on November 27, 2018

https://directaccess.richardhicks.com/2018/11/27/always-on-vpn-and-windows-server-2019-nps-bug/

DirectAccess Manage Out with ISATAP and NLB Clustering

DirectAccess Manage Out with ISATAP and NLB ClusteringDirectAccess connections are bidirectional, allowing administrators to remotely connect to clients and manage them when they are out of the office. DirectAccess clients use IPv6 exclusively, so any communication initiated from the internal network to remote DirectAccess clients must also use IPv6. If IPv6 is not deployed natively on the internal network, the Intrasite Automatic Tunnel Addressing Protocol (ISATAP) IPv6 transition technology can be used to enable manage out.

ISATAP Supportability

According to Microsoft’s support guidelines for DirectAccess, using ISATAP for manage out is only supported for single server deployments. ISATAP is not supported when deployed in a multisite or load-balanced environment.

“Not supported” is not the same as “doesn’t work” though. For example, ISATAP can easily be deployed in single site DirectAccess deployments where load balancing is provided using Network Load Balancing (NLB).

ISATAP Configuration

To do this, you must first create DNS A resource records for the internal IPv4 address for each DirectAccess server as well as the internal virtual IP address (VIP) assigned to the cluster.

DirectAccess Manage Out with ISATAP and NLB Clustering

Note: Do NOT use the name ISATAP. This name is included in the DNS query block list on most DNS servers and will not resolve unless it is removed. Removing it is not recommended either, as it will result in ALL IPv6-enabled hosts on the network configuring an ISATAP tunnel adapter.

Once the DNS records have been added, you can configure a single computer for manage out by opening an elevated PowerShell command window and running the following command:

Set-NetIsatapConfiguration -State Enabled -Router [ISATAP FQDN] -PassThru

DirectAccess Manage Out with ISATAP and NLB Clustering

Once complete, an ISATAP tunnel adapter network interface with a unicast IPv6 address will appear in the output of ipconfig.exe, as shown here.

DirectAccess Manage Out with ISATAP and NLB Clustering

Running the Get-NetRoute -AddressFamily IPv6 PowerShell command will show routes to the client IPv6 prefixes assigned to each DirectAccess server.

DirectAccess Manage Out with ISATAP and NLB Clustering

Finally, verify network connectivity from the manage out host to the remote DirectAccess client.

Note: There is a known issue with some versions of Windows 10 and Windows Server 2016 that may prevent manage out using ISATAP from working correctly. There’s a simple workaround, however. More details can be found here.

Group Policy Deployment

If you have more than a few systems on which to enable ISATAP manage out, using Active Directory Group Policy Objects (GPOs) to distribute these settings is a much better idea. You can find guidance for creating GPOs for ISATAP manage out here.

DirectAccess Client Firewall Configuration

Simply enabling ISATAP on a server or workstation isn’t all that’s required to perform remote management on DirectAccess clients. The Windows firewall running on the DirectAccess client computer must also be configured to securely allow remote administration traffic from the internal network. Guidance for configuring the Windows firewall on DirectAccess clients for ISATAP manage out can be found here.

ISATAP Manage Out for Multisite and ELB

The configuration guidance in this post will not work if DirectAccess multisite is enabled or external load balancers (ELB) are used. However, ISATAP can still be used. For more information about enabling ISATAP manage out with external load balancers and/or multisite deployments, fill out the form below and I’ll provide you with more details.

Summary

Once ISATAP is enabled for manage out, administrators on the internal network can remotely manage DirectAccess clients wherever they happen to be. Native Windows remote administration tools such as Remote Desktop, Windows Remote Assistance, and the Computer Management MMC can be used to manage remote DirectAccess clients. In addition, enterprise administration tools such as PowerShell remoting and System Center Configuration Manger (SCCM) Remote Control can also be used. Further, third-party remote administration tools such as VNC, TeamViewer, LogMeIn, GoToMyPC, Bomgar, and many others will also work with DirectAccess ISATAP manage out.

Additional Information

ISATAP Recommendations for DirectAccess Deployments

DirectAccess Manage Out with ISATAP Fails on Windows 10 and Windows Server 2016 

DirectAccess Client Firewall Rule Configuration for ISATAP Manage Out

DirectAccess Manage Out and System Center Configuration Manager (SCCM)

Contact Me

Interested in learning more about ISATAP manage out for multisite and external load balancer deployments? Fill out the form below and I’ll get in touch with you.

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Thank you for your response. ✨

3 Comments
by Richard M. Hicks on December 14, 2017  •  Permalink
Posted in DirectAccess, DNS and NRPT, IPv6, Load Balancing, Windows Server
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Posted by Richard M. Hicks on December 14, 2017

https://directaccess.richardhicks.com/2017/12/14/directaccess-manage-out-with-isatap-and-nlb-clustering/

Deployment Considerations for DirectAccess on Amazon Web Services (AWS)

Organizations are rapidly deploying Windows server infrastructure with public cloud providers such as Amazon Web Services (AWS) and Microsoft Azure. With traditional on-premises infrastructure now hosted in the cloud, DirectAccess is also being deployed there more commonly.

Supportability

Interestingly, Microsoft has expressly stated that DirectAccess is not formally supported on their own public cloud platform, Azure. However, there is no formal statement of non-support for DirectAccess hosted on other non-Microsoft public cloud platforms. With supportability for DirectAccess on AWS unclear, many companies are taking the approach that if it isn’t unsupported, then it must be supported. I’d suggest proceeding with caution, as Microsoft could issue formal guidance to the contrary in the future.

DirectAccess on AWS

Deploying DirectAccess on AWS is similar to deploying on premises, with a few notable exceptions, outlined below.

IP Addressing

It is recommended that an IP address be exclusively assigned to the DirectAccess server in AWS, as shown here.

Deployment Considerations for DirectAccess on Amazon Web Services (AWS)

Prerequisites Check

When first configuring DirectAccess, the administrator will encounter the following warning message.

“The server does not comply with some DirectAccess prerequisites. Resolve all issues before proceed with DirectAccess deployment.”

The warning message itself states that “One or more network adapters should be configured with a static IP address. Obtain a static address and assign it to the adapter.”

Deployment Considerations for DirectAccess on Amazon Web Services (AWS)

IP addressing for virtual machines are managed entirely by AWS. This means the DirectAccess server will have a DHCP-assigned address, even when an IP address is specified in AWS. Assigning static IP addresses in the guest virtual machine itself is also not supported. However, this warning message can safely be ignored.

No Support for Load Balancing

It is not possible to create load-balanced clusters of DirectAccess servers for redundancy or scalability on AWS. This is because enabling load balancing for DirectAccess requires the IP address of the DirectAccess server be changed in the operating system, which is not supported on AWS. To eliminate single points of failure in the DirectAccess architecture or to add additional capacity, multisite must be enabled. Each additional DirectAccess server must be provisioned as an individual entry point.

Network Topology

DirectAccess servers on AWS can be provisioned with one or two network interfaces. Using two network interfaces is recommended, with the external network interface of the DirectAccess server residing in a dedicated perimeter/DMZ network. The external network interface must use either the Public or Private Windows firewall profile. DirectAccess will not work if the external interface uses the Domain profile. For the Public and Private profile to be enabled, domain controllers must not be reachable from the perimeter/DMZ network. Ensure the perimeter/DMZ network cannot access the internal network by restricting network access in EC2 using a Security Group, or on the VPC using a Network Access Control List (ACL) or custom route table settings.

External Connectivity

A public IPv4 address must be associated with the DirectAccess server in AWS. There are several ways to accomplish this. The simplest way is to assign a public IPv4 address to the virtual machine (VM). However, a public IP address can only be assigned to the VM when it is deployed initially and cannot be added later. Alternatively, an Elastic IP can be provisioned and assigned to the DirectAccess server at any time.

An ACL must also be configured for the public IP that restricts access from the Internet to only inbound TCP port 443. To provide additional protection, consider deploying an Application Delivery Controller (ADC) appliance like the Citrix NetScaler or F5 BIG-IP to enforce client certificate authentication for DirectAccess clients.

Network Location Server (NLS)

If an organization is hosting all of its Windows infrastructure in AWS and all clients will be remote, Network Location Server (NLS) availability becomes much less critical than with traditional on-premises deployments. For cloud-only deployments, hosting the NLS on the DirectAccess server is a viable option. It eliminates the need for dedicated NLS, reducing costs and administrative overhead. If multisite is configured, ensure that the NLS is not using a self-signed certificate, as this is unsupported.

Deployment Considerations for DirectAccess on Amazon Web Services (AWS)

However, for hybrid cloud deployments where on-premises DirectAccess clients share the same internal network with cloud-hosted DirectAccess servers, it is recommended that the NLS be deployed on dedicated, highly available servers following the guidance outlined here and here.

Client Provisioning

All supported DirectAccess clients will work with DirectAccess on AWS. If the domain infrastructure is hosted exclusively in AWS, provisioning clients can be performed using Offline Domain Join (ODJ). Provisioning DirectAccess clients using ODJ is only supported in Windows 8.x/10. Windows 7 clients cannot be provisioned using ODJ and must be joined to the domain using another form of remote network connectivity such as VPN.

Additional Resources

DirectAccess No Longer Supported in Microsoft Azure

Microsoft Server Software Support for Azure Virtual Machines

DirectAccess Network Location Server (NLS) Guidance

DirectAccess Network Location Server (NLS) Deployment Considerations for Large Enterprises

Provisioning DirectAccess Clients using Offline Domain Join (ODJ)

DirectAccess SSL Offload and IP-HTTPS Preauthentication with Citrix NetScaler

DirectAccess SSL Offload and IP-HTTPS Preauthentication with F5 BIG-IP

Planning and Implementing DirectAccess with Windows Server 2016 Video Training Course

Implementing DirectAccess with Windows Server 2016 Book

5 Comments
by Richard M. Hicks on April 24, 2017  •  Permalink
Posted in Azure and AWS, DirectAccess, IPv6, Load Balancing, Windows Server
Tagged , , , , , , , , , , , , , , , , , , , , ,

Posted by Richard M. Hicks on April 24, 2017

https://directaccess.richardhicks.com/2017/04/24/deployment-considerations-for-directaccess-on-amazon-web-services-aws/

DirectAccess Client Firewall Rule Configuration for ISATAP Manage Out

For DirectAccess manage out scenarios, it is necessary to configure the Windows firewall on the DirectAccess client to allow any required inbound communication from the corporate network. For example, if management hosts on the internal network need to initiate Remote Desktop sessions with remote connected DirectAccess clients, the Remote Desktop – User Mode (TCP-In) Windows firewall rule will need to be enabled for the Public and Private profiles.

DirectAccess Client Firewall Rule Configuration for ISATAP Manage Out

While enabling this rule will allow remote desktop connections to be made from the corporate network, its default configuration will also accept remote desktop connections from any network. From a security perspective this is not desirable.

DirectAccess Client Firewall Rule Configuration for ISATAP Manage Out

A better solution is to restrict access to connections originating only from the corporate network. To do this it will be necessary to identify the ISATAP prefix used internally. To determine the corporate ISATAP prefix, run the ipconfig command on a management workstation that is configured for ISATAP. The ISATAP prefix will be the first 96 bits of the IPv6 address assigned to the ISATAP tunnel adapter (essentially everything with the exception of the embedded IPv4 address).

DirectAccess Client Firewall Rule Configuration for ISATAP Manage Out

On the DirectAccess client, right-click the firewall rule and choose Properties. Choose the Scope tab and then select These IP addresses . Click Add and then enter the ISATAP prefix as shown here.

DirectAccess Client Firewall Rule Configuration for ISATAP Manage Out

Once the firewall rule is configured to restrict access to the ISATAP prefix, only corporate management workstations on the internal network will have access to remote DirectAccess clients.

21 Comments
by Richard M. Hicks on April 13, 2015  •  Permalink
Posted in DirectAccess, IPv6, Windows Server
Tagged , , , , , , , , , , ,

Posted by Richard M. Hicks on April 13, 2015

https://directaccess.richardhicks.com/2015/04/13/directaccess-client-firewall-rule-configuration-for-isatap-manage-out/

Windows Server 2012 DirectAccess Network Location Server Not Working Properly

After configuring a Windows Server 2012 DirectAccess server to use an intranet-based Network Location Server (NLS), you may notice that the operations status in the remote access management console indicates a critical problem with NLS, when in fact you can browse the NLS server from the DirectAccess server.

DirectAccess Network Location Server Issue

The issue here is that the DirectAccess server, in addition to being able to successfully connect to the NLS using an HTTP GET, must also be able to ping the NLS server. However, inbound ICMP is often blocked on web servers which results in the DirectAccess server marking the service as failed. The issue can be quickly resolved by modifying the host firewall policy to allow inbound ICMPv4 echo requests. For example, in my test lab I’m using a Microsoft Windows Server 2012 server with Internet Information Services (IIS) installed. A new access rule can be added to the Windows Firewall with Advanced Security (WFAS) by executing the following PowerShell command:

New-NetFirewallRule -Name “Allow Inbound ICMPv4 Echo Request” -DisplayName “Allow Inbound ICMPv4 Echo Request” -Protocol ICMPv4 -IcmpType 8 -RemoteAddress 172.16.1.241, 172.16.1.242 -Profile Domain -Action Allow -Enabled True

Note that my lab server is domain joined, so I’ve specified the WFAS profile to be the Domain profile. In addition I’ve included the IPv4 addresses assigned to the internal network interfaces of my two DirectAccess servers. You’ll need change the command as required to work in your environment.

35 Comments
by Richard M. Hicks on July 22, 2013  •  Permalink
Posted in Windows Server
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Posted by Richard M. Hicks on July 22, 2013

https://directaccess.richardhicks.com/2013/07/22/windows-server-2012-directaccess-network-location-server-not-working-properly/