One Identity Safeguard for Privileged Sessions 6.0.9 - Administration Guide

Troubleshooting Citrix-related problems

Accessing Citrix servers using the Remote Desktop Protocol

Accessing Citrix servers using the Remote Desktop Protocol may fail in certain situations, and the connection is terminated with the ERROR: error while decompressing packet error message on the client, or with the Event56, TermDD, The Terminal Server security layer detected an error in the protocol stream and has disconnected the client. message on the server.

To overcome this problem, modify the settings of the network card of the server, and disable the Large Send Offload option.

RDP-specific settings

The following sections describe configuration settings available only for the RDP protocol. Use the following policies to control who, when, and how can access the RDP connection.

• Channel Policy: The channel policy determines which RDP channels (for example clipboard, file-sharing, and so on) can be used in the connection, and whether they are audited or not. The different channels may be available only under certain restrictions, as set in the channel policy. For details, see Creating and editing channel policies.

• RDP settings: RDP settings determine the parameters of the connection on the protocol level, including timeout value, display parameters, and the version of RDP permitted. For details, see Creating and editing protocol-level RDP settings.

• Domain membership: When using Network Level Authentication (CredSSP) One Identity Safeguard for Privileged Sessions (SPS) must be a member of the domain. For details, see Network Level Authentication (NLA) with domain membership.

• TLS-encrypted connections: For details on how to setup TLS-encrypted RDP connections, see Enabling TLS-encryption for RDP connections and Verifying the certificate of the RDP server in encrypted connections.

• SPS as a Remote Desktop Gateway: For details on how to configure SPS to accept connections using the Remote Desktop Gateway Server Protocol, see Using One Identity Safeguard for Privileged Sessions (SPS) as a Remote Desktop Gateway.

• Content Policy: Content policies allow you to inspect the content of the connections for various text patterns, and perform an action if the pattern is found. For example, SPS can send an e-mail alert if a specific window title appears in RDP and VNC connections. For details, see Creating a new content policy.

• Authentication and Authorization plugin:

  One Identity Safeguard for Privileged Sessions (SPS) provides a plugin framework to integrate SPS to external systems to authenticate or authorize the user before authenticating on the target server. Such plugins can also be used to request additional information from the users, for example, to perform multi-factor authentication.

  For details, see Integrating external authentication and authorization systems.

Using multiple monitors (Multimon) is supported. To enable Multimon, use one of the following three methods:

• enable Display > Use all my monitors for the remote session option in the Remote Desktop Client (mstsc.exe) window of the client machine

• use the /multimon switch on the mstsc.exe command line

• add the use multimon:i:1 row to the RDP file

Limitations

The RDP connection fails due to the following Windows-side settings:

• If the target user is a member of the Protected Users security group.
• If Remote Credential Guard is enabled and used.
• If Restricted Admin mode is enabled and used. For more information on how to enable or disable the Restricted Admin mode on Windows, see Remote Desktop Services: Enable Restricted Admin mode.

Supported RDP channel types

The available RDP channel types and their functionalities are described below. For details on configuring Channel Policies, see Creating and editing channel policies. For a list of supported client applications, see Supported protocols and client applications.

• Drawing: Enables access to the server's graphical desktop (screen). This channel must be enabled for RDP to work.

  NOTE: In case the Drawing channel is disabled and the load of One Identity Safeguard for Privileged Sessions (SPS) is high, or the connection requires four-eyes authorization and the Authorizer is slow to accept the connection, the client might receive the following error message: The Remote Desktop Gateway server administrator has ended the connection. Try reconnecting later or contact your network administrator for assistance

• Clipboard: Enables access to the server's clipboard: the clipboard of the remote desktop can be pasted into local applications (and vice-versa). Note that SPS can audit the clipboard channel, and that files transferred via the clipboard can be audited Configuring SPS to enable exporting files from audit trails after RDP file transfer via clipboard.

  If the Clipboard channel is enabled, it implicitly enables copying files as well, as the user can simply copy-paste the file. Copy-pasted files will not be visible in the logs or the File operations column of the Search page. To ensure that SPS records file transfer events, you must disable the Clipboard channel.

• Redirects: Enables access to every device redirection available in RDP, like file-sharing, printer sharing, device (for example, CD-ROM) sharing, and so on.

  • To make the list of file operations available in the File operations column of the Search page, navigate to the Channel Policies page of the protocol, and enable the Log file transfers to database option. This option is disabled by default.

  • To send the file operations into the system log, enable the Log file transfers to syslog option. This option is disabled by default.

    NOTE: Turning logging on might result in a slight performance penalty. If traffic load slows processes down, disable the option.

  To enable only specific types of redirections, use the following channels:

  • Serial redirect: Enables access to serial-port redirections.

  • Parallel redirect: Enables access to parallel-port redirections.

  • Printer redirect: Enables access to shared printers.

    When enabling printer redirection, you may need to use TSVCTKT and XPSRD channels — these enable XPS printing.

    Note that these channels are dynamic virtual channels and you have to be enable them using the Custom channel type.

    For more information on TSVCTKT and XPSRD channels, see section 2.1 Transport in Microsoft Technical Document [MS-RDPEXPS].

    Before consulting the cited Microsoft Technical Document, it is recommended to start by reading [MS-RDSOD]: Remote Desktop Services Protocols Overview.

  • Disk redirect: Enables access to shared disk drives.

    • To make the list of file operations available in the File operations column of the Search page, navigate to the Channel Policies page of the protocol, and enable the Log file transfers to database option. This option is disabled by default.

    • To send the file operations into the system log, enable the Log file transfers to syslog option. This option is disabled by default.

      NOTE: Turning logging on might result in a slight performance penalty. If traffic load slows processes down, disable the option.

    If the Clipboard channel is enabled, it implicitly enables copying files as well, as the user can simply copy-paste the file. Copy-pasted files will not be visible in the logs or the File operations column of the Search page. To ensure that SPS records file transfer events, you must disable the Clipboard channel.

  • SCard redirect: Enables access to shared SCard devices.

  To permit only specific redirections, enter the unique name of the redirection into the Details field. For example, if you want to enable access only to the shared disk drive C:, enable the Disk redirect channel and enter C: into the Permitted devices field. Note that the name of the device comes from the device itself, so it is case sensitive, and may not always be reliable from a security point of view.

• Sound: Enables access to the sound device of the server.

• Custom: Applications can open custom channels to the clients connecting remotely to the server. Enabling the Custom channel allows the clients to access all of these custom channels. To permit only specific channels, enter the unique names of the channel into the Permitted devices field.

  For example, to monitor RemoteApp connections, you need to configure custom channels. For more information, see Configuring RemoteApps.

• Seamless: Enables seamless channels that run a single application on the RDP server, instead of accessing the entire desktop.

• Dynamic virtual channel: Enables the server to open channels back to the client dynamically. To restrict which dynamic channels are permitted, select Channel details, click and enter the name of the permitted channel.

  Additionally, you may need to use one or more of the following:

  • PNPDR and FileRedirectorChannel channels: Enable Plug and Play devices.

    For more information, see section 2.1 Transport in Microsoft Technical Document [MS-RDPEPNP].

  • URBDRC channels: Enable USB redirection.

    For more information, see section 2.1 Transport in Microsoft Technical Document [MS-RDPEUSB].

  Before consulting any of the listed Microsoft Technical Documents, it is recommended to start by reading [MS-RDSOD]: Remote Desktop Services Protocols Overview.

Creating and editing protocol-level RDP settings

RDP settings determine the parameters of the connection on the protocol level. For example, timeout value, the version of RDP permitted in the connection, and display parameters.

Figure 177: RDP Control > Settings — RDP settings

To create a new RDP settings profile or edit an existing one

1. Navigate to RDP Control > Settings and click to create an RDP setting profile. Enter a name for the profile (for example, rdp5only).

2. Click to display the parameters of the RDP connection.

3. Modify the parameters as needed. The following parameters are available:

   • Idle timeout: Timeout value for the connection in seconds. To avoid early timeout, set it to a larger value, for example a week (604800 seconds).

     Caution: Determining if a connection is idle is based on the network traffic generated by the connection, not the activity of the user. For example, if an application or the taskbar of a graphical desktop displays the time which is updated every minute, it generates network traffic every minute, negating the effects of timeout values greater than one minute and preventing One Identity Safeguard for Privileged Sessions (SPS) from closing the connection.

     Caution: If the value is set below 31 seconds, MSTSC can fail and prevent new connections if Act as a Remote Desktop Gateway is enabled in RDP Control > Connections. To prevent this, set the Idle timeout value to at least 31 seconds.

   • Maximum display width: The maximum allowed width of the remote desktop in pixels (for example 1024).

     NOTE: The Maximum display width and Maximum display height options should be high enough to cover the combined resolution of the client monitor setup. Connections that exceed these limits will automatically fail. Make sure to adjust these settings if your clients use multiple monitors. For example, if your clients use two monitors that have a resolution of 1920x1080 pixels each, set Maximum display width to 4000, and Maximum display height to 2200.

   • Maximum display height: The maximum allowed height of the remote desktop in pixels (for example 768).

     NOTE: The Maximum display width and Maximum display height options should be high enough to cover the combined resolution of the client monitor setup. Connections that exceed these limits will automatically fail. Make sure to adjust these settings if your clients use multiple monitors. For example, if your clients use two monitors that have a resolution of 1920x1080 pixels each, set Maximum display width to 4000, and Maximum display height to 2200.

   • Maximum display depth: The maximum allowed color depth the remote desktop in bits (for example 24). The following values are valid: 8, 15, 16, 24.

     Caution: Using 32-bit color depth is currently not supported: client connections requesting 32-bit color depth automatically revert to 24-bit. Certain Windows versions do not support 24-bit color depth. In this case, those versions can only be displayed in 16-bit color depth. SPS automatically changes its settings to 16-bit.

   • Enable Network Level Authentication: Select this option to enable the use of Network Level Authentication (NLA, also called Credential Security Service Provider or CredSSP).

     • If you enable this option, you have to configure SPS to join your domain. If you use a domain, then the target servers and SPS must be in the same domain, or you must establish trust between the domains that contain the target servers and SPS. For details on the type of trust required, see Using One Identity Safeguard for Privileged Sessions (SPS) across multiple domains. For details on configuring SPS to join a domain, see Network Level Authentication (NLA) with domain membership.

     • If you cannot or do not want to join SPS to the domain, see Network Level Authentication without domain membership.

     Note the following points:

     • SSL-encrypted connections do not require this option, it is only needed for Network Level Authentication (NLA).

     • Smartcard authentication cannot be used when the Enable Network Level Authentication option is enabled.

     Caution: To access hosts running Windows 2008 Server R2 using Network Level Authentication (NLA), select the Enable RDP4 style authentication option as well.

   • Enable RDP4 style authentication: Select this option to enable RDP4 authentication within the RDP5 protocol. This might be needed for compatibility reasons with certain client applications.

   • Enable pre channel check: Select this option to evaluate the connection and channel policies before establishing the server-side connection. That way if the connection is not permitted at all, SPS does not establish the server-side connection.

   • Permit unreliable usernames: SPS automatically terminates RDP connections if it cannot reliably extract the username from the RDP connection. Enable this option to permit connections with unreliable usernames. For details on ensuring that the usernames in RDP connections are reliable, see Usernames in RDP connections.

     Known issue

     When accessing a Windows Server 2003 R2 host, the Permit unreliable usernames option is disabled, and the username is unreliable, SPS terminates the connection, but only after the user logs in. As a result, the session is not closed on the server-side.

   • Autologon domain suffix: Enter the suffix that the client will append to the domain when using autologon in conjunction with Network Level Authentication (CredSSP).

4. To display a banner message to the clients before authentication, enter the message into the Banner field. For example, this banner can inform the users that the connection is audited. SPS displays this banner in a graphical window that has only an OK button. Note the following points:

   • You can write a plain-text or a basic HTML-formatted banner.

     Caution: If the banner is overly complex HTML using deeply embedded structures, displaying the banner will fail, causing the RDP connections to time out.

   • When using HTML markup, the entire banner must be a single HTML object (for example, a div).

     <div align="center"><b>Your session is recorded using Privileged Session Monitoring</b></div>

   • In HTML, you can embed images (for example, a company logo) as data URLs in an img tag:

     To include a logo or other image, use a base64-encoded data url within an, like this: <img alt="Embedded Image" src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAADIA..." />.

   • Note that while you can include links in the text, your users cannot click or copy them.

5. To configure TLS security settings on both the Client side and the Server side, proceed to TLS security settings.

   Figure 178: <Protocol> Control > Settings > TLS security settings - configuring TLS security settings

   

   • Cipher strength specifies the cipher string OpenSSL will use. The following settings options are possible:

     • Recommended: this setting only uses ciphers with adequate security level.

     • Custom: this setting allows you to specify the list of ciphers you want to permit SPS to use in the connection. This setting is only recommended in order to ensure compatibility with older systems. For more details on customizing this list, check the 'openssl-ciphers' manual page on your SPS appliance.

       For example: ALL:!aNULL:@STRENGTH

   • Minimum TLS version specifies the minimal TLS version SPS will offer during negotiation. The following settings options are possible:

     • TLS 1.2: this setting will only offer TLS version 1.2 during negotiation. This is the recommended setting.

     • TLS 1.1: this setting will offer TLS version 1.1 and later versions during negotiation.

     • TLS 1.0: this setting will offer TLS version 1.0 and later versions during negotiation.

   NOTE: Note that SPS only permits TLS-encrypted connections. SSLv3 is not supported.

   NOTE: TLS 1.1 and 1.2 support for Windows 7 Service Pack 1 (SP1) and for Windows Server 2008 R2 Service Pack 2 (SP2) is not available by default. For more information about the requirements and process of enabling this feature, click here or contact our Support Team.

6. Click .

7. Select this settings profile in the RDP settings field of your connections.