Remote Desktop Protocol

Remote Desktop Protocol (RDP) is a proprietary protocol developed by Microsoft, which provides a user with a graphical interface to connect to another computer over a network connection. The user employs RDP client software for this purpose, while the other computer must run RDP server software.

Clients exist for most versions of Microsoft Windows (including Windows Mobile), Linux, Unix, macOS, iOS, Android, and other operating systems. RDP servers are built into Windows operating systems; an RDP server for Unix and OS X also exists. By default, the server listens on TCP port 3389[1] and UDP port 3389.[2]

Microsoft currently refers to their official RDP client software as Remote Desktop Connection, formerly "Terminal Services Client".

The protocol is an extension of the ITU-T T.128 application sharing protocol.[3]

History

Every version of Microsoft Windows from Windows XP onwards[4] includes an installed Remote Desktop Connection (RDC) ("Terminal Services") client (mstsc.exe) whose version is determined by that of the operating system or by the last applied Windows Service Pack. The Terminal Services server is supported as an official feature on Windows NT 4.0 Terminal Server Edition, Windows 2000 Server, all editions of Windows XP except Windows XP Home Edition, Windows Server 2003, Windows Home Server, on Windows Fundamentals for Legacy PCs, in Windows Vista Ultimate, Enterprise and Business editions, Windows Server 2008 and Windows Server 2008 R2 and on Windows 7 Professional and above.

Microsoft provides the client required for connecting to newer RDP versions for downlevel operating systems. Since the server improvements are not available downlevel, the features introduced with each newer RDP version only work on downlevel operating systems when connecting to a higher version RDP server from these older operating systems, and not when using the RDP server in the older operating system.

Version 4.0

Based on the ITU-T T.128 application sharing protocol (during draft also known as "T.share") from the T.120 recommendation series, the first version of RDP (named version 4.0) was introduced by Microsoft with "Terminal Services", as a part of their product Windows NT 4.0 Server, Terminal Server Edition. The Terminal Services Edition of NT 4.0 relied on Citrix's MultiWin technology, previously provided as a part of Citrix WinFrame atop Windows NT 3.51, in order to support multiple users and login sessions simultaneously. Microsoft required Citrix to license their MultiWin technology to Microsoft in order to be allowed to continue offering their own terminal-services product, then named Citrix MetaFrame, atop Windows NT 4.0. The Citrix-provided DLLs included in Windows NT 4.0 Terminal Services Edition still carry a Citrix copyright rather than a Microsoft copyright. Later versions of Windows integrated the necessary support directly. The T.128 application sharing technology was acquired by Microsoft from UK software developer Data Connection Limited.[5][6]

Version 5.0

This version was introduced with Windows 2000 Server, added support for a number of features, including printing to local printers, and aimed to improve network bandwidth usage.

Version 5.1

This version was introduced with Windows XP Professional and included support for 24-bit color and sound. The client is available for Windows 2000, Windows 9x, Windows NT 4.0.[7] With this version, the name of the client was changed from Terminal Services Client to Remote Desktop Connection; the heritage remains to this day, however, as the underlying executable is still named mstsc.exe.

Version 5.2

This version was introduced with Windows Server 2003, included support for console mode connections, a session directory, and local resource mapping. It also introduces Transport Layer Security (TLS) 1.0 for server authentication, and to encrypt terminal server communications.[8] This version is built into Windows XP Professional x64 Edition and Windows Server 2003 x64 & x86 Editions.

Version 6.0

This version was introduced with Windows Vista and incorporated support for Windows Presentation Foundation applications, Network Level Authentication, multi-monitor spanning and large desktop support, and TLS 1.0 connections.[9] Version 6.0 client is available for Windows XP SP2, Windows Server 2003 SP1/SP2 (x86 and x64 editions) and Windows XP Professional x64 Edition. Microsoft Remote Desktop Connection Client for Macintosh OS X is also available with support for Intel and PowerPC Mac OS versions 10.4.9 and greater.

Server 2012 can support RDC 6.0 or later.

Version 6.1

This version was released in February 2008 and is included with Windows Server 2008, as well as with Windows Vista Service Pack 1. The client is included with Windows XP SP3.[10] In addition to changes related to how a remote administrator connects to the "console",[11] this version has new functionality introduced in Windows Server 2008, such as connecting remotely to individual programs and a new client-side printer redirection system that makes the client's print capabilities available to applications running on the server, without having to install print drivers on the server.[12][13]

Version 7.0

This version was released to manufacturing in July 2009 and is included with Windows Server 2008 R2, as well as with Windows 7.[14] With this release, also changed from Terminal Services to Remote Desktop Services. This version has new functions such as Windows Media Player redirection, bidirectional audio, multi-monitor support, Aero glass support, enhanced bitmap acceleration, Easy Print redirection,[15] Language Bar docking. The RDP 7.0 client is available on Windows XP SP3 and Windows Vista SP1/SP2 through KB969084.[16] RDP 6.1 client and RDP 7.0 client are not supported on Windows Server 2003 x86 and Windows Server 2003 / Windows XP Professional x64 editions. RDP 7.0 is also not supported on Windows Server 2008. RDP 7.0 clients also do not support connecting to terminal servers running Windows 2000 Server.[17]

Most RDP 7.0 features like Aero glass remote use, bidirectional audio, Windows Media Player redirection, multiple monitor support and Remote Desktop Easy Print are only available in Windows 7 Enterprise or Ultimate editions.[18][19]

SP1 and Server 2008 R2 SP1. It adds RemoteFX functionality.

Version 8.0

This version was released in Windows 8 and Windows Server 2012. This version has new functions such as Adaptive Graphics (progressive rendering and related techniques), automatic selection of TCP or UDP as transport protocol, multi touch support, DirectX 11 support for vGPU, USB redirection supported independently of vGPU support, etc.[20][21] A "connection quality" button is displayed in the RDP client connection bar for RDP 8.0 connections; clicking on it provides further information about connection, including whether UDP is in use or not.[22]

The RDP 8.0 client and server components are also available as an add-on for Windows 7 SP1. The RDP 8.0 client is also available for Windows Server 2008 R2 SP1, but the server components are not. The add-on requires the DTLS protocol to be installed as prerequisite.[22] After installing the updates, for the RDP 8.0 protocol to be enabled between Windows 7 machines, an extra configuration step is needed using the Group Policy editor.[23]

A new feature in RDP 8.0 is limited support for RDP session nesting; it only works for Windows 8 and Server 2012 though, Windows 7 and Server 2008 R2 (even with the RDP 8.0 update) do not support this feature.[24]

The "shadow" feature from RDP 7, which allowed an administrator to monitor (snoop) on a RDP connection has been removed in RDP 8. The Aero Glass remoting feature (applicable to Windows 7 machines connecting to each other) has also been removed in RDP 8.[21][22]

Version 8.1

This version was released with Windows 8.1 and Windows Server 2012 R2. A RDP 8.1 client update exists for Windows 7 SP1 as well, but unlike the RDP 8.0 update for Windows 7, it does not add a RDP 8.1 server component to Windows 7. Furthermore, if RDP 8.0 server function is desired on Windows 7, the KB 2592687 (RDP 8.0 client and server components) update must be installed before installing the RDP 8.1 update.[25][26]

Support for session shadowing was added back in RDP version 8.1. This version also fixes some visual glitches with Microsoft Office 2013 when running as a RemoteApp.[25]

Version 8.1 of the RDP also enables a "restricted admin" mode. Logging into this mode only requires knowledge of the hashed password, rather than of its plaintext, therefore making a pass the hash attack possible.[27] Microsoft has released an 82-page document explaining how to mitigate this type of attack.[28]

Version 10.0

Version 10.0 of the RDP includes the following new features: AutoSize zoom (useful for HiDPI clients).[29] In addition graphics compression improvements were included utilizing H.264/AVC.[30]

Features

  • 32-bit color support. 8-, 15-, 16-, and 24-bit color are also supported.
  • 128-bit encryption, using the RC4 encryption algorithm, as of Version 6.[31]
  • Audio Redirection allows users to process audio on a remote desktop and have the sound redirected to their local computer.
  • File System Redirection allows users to use their local files on a remote desktop within the terminal session.
  • Printer Redirection allows users to use their local printer within the terminal session as they would with a locally- or network-shared printer.
  • Port Redirection allows applications running within the terminal session to access local serial and parallel ports directly.
  • The remote computer and the local computer can share the clipboard.

Microsoft introduced the following features with the release of RDP 6.0 in 2006:

  • Seamless Windows: remote applications can run on a client machine that is served by a Remote Desktop connection. It is available since RDP 6.[32]
  • Remote Programs: application publishing with client-side file-type associations.
  • Terminal Services Gateway: enables the ability to use a front-end IIS server to accept connections (over port 443) for back-end Terminal Services servers via an https connection, similar to how RPC over https allows Outlook clients to connect to a back-end Exchange 2003 server. Requires Windows Server 2008.
  • Network Level Authentication
  • Support for remoting the Aero Glass Theme (or Composed Desktop), including ClearType font-smoothing technology.
  • Support for remoting Windows Presentation Foundation applications: compatible clients that have .NET Framework 3.0 support can display full Windows Presentation Foundation effects on a local machine.
  • Rewrite of device redirection to be more general-purpose, allowing a greater variety of devices to be accessed.
  • Fully configurable and scriptable via Windows Management Instrumentation.
  • Improved bandwidth tuning for RDP clients.
  • Support for Transport Layer Security (TLS) 1.0 on both server and client ends (can be negotiated if both parties agree, but not mandatory in a default configuration of any version of Windows).
  • Multiple monitor support for allowing one session to use multiple monitors on the client (disables desktop composition)

Release 7.1 of RDP in 2010 introduced the following feature:

  • RemoteFX: RemoteFX provides virtualized GPU support and host-side encoding; it ships as part of Windows Server 2008 R2 SP1.

Security issues

Version 5.2 of the RDP in its default configuration is vulnerable to a man-in-the-middle attack. Administrators can enable transport layer encryption to mitigate this risk.[33][34]

RDP sessions are also susceptible to in-memory credential harvesting, which can be used to launch pass the hash attacks.

In March 2012, Microsoft released an update for a critical security vulnerability in the RDP. The vulnerability allowed a Windows computer to be compromised by unauthenticated clients and computer worms.[35]

RDP client version 6.1 can be used to reveal the names and pictures of all users on the RDP Server (no matter which Windows version) in order to pick one, if no username is specified for the RDP connection.

In March 2018 Microsoft released a patch for CVE-2018-0886, a remote code execution vulnerability in CredSSP, which is a Security Support Provider involved in the Microsoft Remote Desktop and Windows Remote Management, discovered by Preempt.[36][37]

Non-Microsoft implementations

There are numerous non-Microsoft implementations of RDP clients and servers that implement subsets of the Microsoft functionality. For instance, the open-source command-line client rdesktop is available for Linux/Unix and Microsoft Windows operating systems. There are many GUI clients, like tsclient and KRDC, that are built on top of rdesktop; CoRD is such a client for the Macintosh.

In 2009, rdesktop was forked as FreeRDP, a new project aiming at modularizing the code, addressing various issues, and implementing new features.[38] FreeRDP comes with its own command-line-client xfreerdp, which supports Seamless Windows in RDP6. There’s also a GTK-Application named Remmina.

An open-source implementation of a Remote Desktop Protocol server on Unix is FreeRDP and xrdp. The Windows' Remote Desktop Connection client can be used to connect to a server. Proprietary RDP client solutions such as rdpclient are available as a stand-alone application or embedded with client hardware.

A new access paradigm, browser-based access, has enabled users to access Windows desktops and applications on any RDP hosts, such as Microsoft Remote Desktop (RDS) Session Hosts (Terminal Services) and virtual desktops, as well as remote physical PCs.

There is also a so-called VRDP used in the VirtualBox virtual machine implementation by Oracle. This protocol is compatible with all RDP clients, such as that provided with Windows but, unlike the original RDP, can be configured to accept unencrypted and password unprotected connections, which may be useful in secure and trusted networks, such as home or office LANs. By default, Microsoft's RDP server refuses connections to user accounts with empty passwords (but this can be changed with the Group Policy Editor[39]). External and guest authorization options are provided by VRDP as well. It does not matter which operating system is installed as a guest because VRDP is implemented on the virtual machine (host) level, not in the guest system. The proprietary VirtualBox Extension Pack is required.

Patents

Microsoft requires third-party implementations to license the relevant RDP patents.[40] As of February 2014, the extent to which open-source clients meet this requirement remains unknown.

See also

References

  1. ↑ "How to change the listening port for Remote Desktop". Microsoft. January 31, 2007. Retrieved November 2, 2007. Microsoft KB article 306759, revision 2.2.
  2. ↑ "Service Name and Transport Protocol Port Number Registry". Internet Assigned Numbers Authority. January 9, 2015. Retrieved January 13, 2015.
  3. ↑ http://www.rdesktop.org/#docs
  4. ↑ Microsoft. "Connecting to another computer Remote Desktop Connection". Retrieved 2012-12-22.
  5. ↑ "Metaswitch – History". Network-technologies.metaswitch.com. Retrieved 2014-02-13.
  6. ↑ Implementing Collaboration Technologies in Industry, Bjørn Erik Munkvold, 2003; Chapter 7
  7. ↑ "Windows XP Remote Desktop Connection software [XPSP2 5.1.2600.2180]". Microsoft.com. 2012-08-27. Retrieved 2014-03-11.
  8. ↑ "Configuring authentication and encryption". January 21, 2005. Retrieved March 30, 2009. Microsoft Technet article
  9. ↑ "Remote Desktop Connection (Terminal Services Client 6.0)". June 8, 2007. Retrieved June 20, 2007. Microsoft KB article 925876, revision 7.0.
  10. ↑ "Description of the Remote Desktop Connection 6.1 client update for Terminal Services in Windows XP Service Pack 2". microsoft. Retrieved 2014-03-11.
  11. ↑ "Changes to Remote Administration in Windows Server 2008". Terminal Services Team Blog. Microsoft. December 17, 2007. Retrieved February 10, 2008.
  12. ↑ "Terminal Services Printing". TechNet – Windows Server 2008 Technical Library. Agozik-Microsoft. January 10, 2008. Archived from the original on January 21, 2014. Retrieved February 10, 2008.
  13. ↑ "Introducing Terminal Services Easy Print: Part 1 – Remote Desktop Services (Terminal Services) Team Blog – Site Home – MSDN Blogs". Blogs.msdn.com. Retrieved 2014-02-13.
  14. ↑ "Remote Desktop Connection 7 for Windows 7, Windows XP & Windows Vista". Terminal Services Team Blog. Microsoft. August 21, 2009. Archived from the original on August 27, 2009. Retrieved August 21, 2009.
  15. ↑ "Using Remote Desktop Easy Print in Windows 7 and Windows Server 2008 R2". Blogs.msdn.com. Retrieved 2014-03-11.
  16. ↑ "Announcing the availability of Remote Desktop Connection 7.0 for Windows XP SP3, Windows Vista SP1, and Windows Vista SP2". Blogs.msdn.com. Archived from the original on March 8, 2010. Retrieved March 11, 2014.
  17. ↑ "Remote Desktop Connection Client 7.0 does not support accessing Windows 2000 servers". Technet.microsoft.com. 2010-07-13. Retrieved 2014-03-11.
  18. ↑ "Aero Glass Remoting in Windows Server 2008 R2". Blogs.msdn.com. Archived from the original on June 27, 2009. Retrieved March 11, 2014.
  19. ↑ "Remote Desktop Connection 7 for Windows 7, Windows XP & Windows Vista". Blogs.msdn.com. Archived from the original on August 27, 2009. Retrieved March 11, 2014.
  20. ↑ "Windows Server 2012 Remote Desktop Services (RDS) – Windows Server Blog – Site Home – TechNet Blogs". Blogs.technet.com. Retrieved 2014-02-13.
  21. 1 2 "How Microsoft RDP 8.0 addresses WAN, graphics shortcomings". Searchvirtualdesktop.techtarget.com. Retrieved 2014-02-13.
  22. 1 2 3 "Remote Desktop Protocol (RDP) 8.0 update for Windows 7 and Windows Server 2008 R2". Support.microsoft.com. Retrieved 2014-02-13.
  23. ↑ "Get the best RDP 8.0 experience when connecting to Windows 7: What you need to know – Remote Desktop Services (Terminal Services) Team Blog – Site Home – MSDN Blogs". Blogs.msdn.com. Retrieved 2014-02-13.
  24. ↑ "Running a Remote Desktop Connection session within another Remote Desktop Connection session is supported with Remote Desktop Protocol 8.0 for specific scenarios". Support.microsoft.com. 2012-11-02. Retrieved 2014-02-13.
  25. 1 2 "Update for RemoteApp and Desktop Connections feature is available for Windows". Support.microsoft.com. 2014-02-11. Retrieved 2014-03-11.
  26. ↑ "Remote Desktop Protocol 8.1 Update for Windows 7 SP1 released to web – Remote Desktop Services (Terminal Services) Team Blog – Site Home – MSDN Blogs". Blogs.msdn.com. Retrieved 2014-02-13.
  27. ↑ "New "Restricted Admin" feature of RDP 8.1 allows pass-the-hash". Labs.portcullis.co.uk. 2013-10-20. Retrieved 2014-03-11.
  28. ↑ "Mitigating Pass-the-Hash (PtH) Attacks and Other Credential Theft Techniques". Microsoft.com. Retrieved 2014-03-11.
  29. ↑ "The Microsoft Platform: Remote Desktop Protocol 10, zoom option to support remoting into Windows 7 with hiDPI client". Microsoft.com. Retrieved 2015-01-12.
  30. ↑ "Remote Desktop Protocol (RDP) 10 AVC/H.264 improvements in Windows 10 and Windows Server 2016 Technical Preview". Microsoft.com. Retrieved 2016-01-12.
  31. ↑ "Remote Desktop Protocol". Microsoft. Retrieved March 30, 2009.
  32. ↑ "[MS-RDPERP]: Remote Desktop Protocol: Remote Programs Virtual Channel Extension". Msdn.microsoft.com. Retrieved 2014-02-13.
  33. ↑ "National Vulnerability Database (NVD) National Vulnerability Database (CVE-2005-1794)". Web.nvd.nist.gov. 2011-07-19. Retrieved 2014-02-13.
  34. ↑ "Configuring Terminal Servers for Server Authentication to Prevent "Man in the Middle" Attacks". Microsoft. July 12, 2008.
  35. ↑ "Microsoft Security Bulletin MS12-020 – Critical". Microsoft. 13 March 2012. Retrieved 16 March 2012.
  36. ↑ "https://portal.msrc.microsoft.com/en-us/security-guidance/advisory/CVE-2018-0886". portal.msrc.microsoft.com. Retrieved 2018-03-23. External link in |title= (help)
  37. ↑ Karni, Eyal. "From Public Key to Exploitation: How We Exploited the Authentication in MS-RDP". Retrieved 2018-03-23.
  38. ↑ FreeRDP is a successor to rdesktop, a longtime-favored application for use on *nix systems to access Windows servers and workstations. The goal of FreeRDP is twofold: a more complete support of keyboard layouts; and support of newer Remote Desktop Protocol (RDP) features found in the Windows 6.0(Vista/2008) & 6.1 (7/2008R2) environments.(from README)
  39. ↑ Bens, Jelle (2010-01-31). "Jelle Bens: Windows 7 RDP with blank password". Jellebens.blogspot.ru. Retrieved 2014-03-11.
  40. ↑ "Remote Desktop Protocol Licensing Available for RDP 8". Blogs.msdn.com. 2014-12-11. Archived from the original on 2018-02-08. Retrieved 2018-02-08.

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