MS02-051: Cryptographic Flaw in RDP Protocol Can Cause Information Disclosure

Windows-based computers use Remote Desktop Protocol (RDP) to provide remote terminal sessions to clients. The protocol transmits information about a terminal session's keyboard, mouse, and video to the remote client. This protocol is used by Terminal Services in Microsoft Windows NT 4.0 and Windows 2000, and by Remote Desktop in Windows XP. Two security vulnerabilities, both of which are corrected by the patch that is described in this article, have been discovered in various RDP implementations.

The first vulnerability involves the way in which session encryption is implemented in certain versions of RDP. All RDP implementations permit the data in an RDP session to be encrypted. However, in the versions of RDP that are included in Windows 2000 and Windows XP, the checksums for the plain-text session data are sent without themselves being encrypted. An attacker who can "eavesdrop on" and record an RDP session might be able to conduct a straightforward cryptanalytic attack against the checksums and to recover the session traffic.

The second vulnerability involves the way in which the RDP implementation in Windows XP handles data packets that are malformed in a particular way. When RDP receives such data packets, the Remote Desktop service stops working. When this problem occurs, Windows stops working correctly also. An attacker does not have to be authenticated on an affected computer to deliver packets of this type to an affected computer.

NOTE: By default, RDP sessions are enabled in Windows NT 4.0 Terminal Server Edition, but not in any other version of Windows. However, neither of these vulnerabilities occur in Windows NT 4.0 Terminal Server Edition.

Windows XP

To resolve this problem, obtain the latest service pack for Windows XP, or obtain the individual update for this specific problem. For additional information about the service pack, click the article number below to view the article in the Microsoft Knowledge Base:

Individual Update Download Information

The following files are available for download from the Microsoft Download Center:

Windows XP Professional and Windows XP Home Edition: Windows XP 64-Bit Edition: Release Date: September 18, 2002

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.

Installation Information

You must restart your computer after you apply this update. This update supports the following Setup switches:

• /? Display the list of installation switches.
• /u Unattended mode.
• /f Force other programs to quit when the computer shuts down.
• /n Do not back up files for removal.
• /o Overwrite OEM files without prompting.
• /z Do not restart when installation is complete.
• /q Quiet mode (no user interaction).
• /l List installed hotfixes.
• /x Extracts the files without running Setup.

For example, the following command line installs the update without any user intervention and then does not force the computer to restart: WARNING: Your computer is vulnerable until you restart it.

File Information

The English version of this fix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

The following files are installed in the %Windir%\System32\Drivers folder:

Windows 2000 Service Pack Information

To resolve this problem, obtain the latest service pack for Microsoft Windows 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

Windows 2000 Hotfix Information

A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that you determine are at risk of attack. Evaluate your computer's physical accessibility, network and Internet connectivity, and other factors to determine the degree of risk to your computer. See the associated Microsoft Security Bulletin to help determine the degree of risk. This fix may receive additional testing. If your computer is sufficiently at risk, Microsoft recommends that you apply this fix now. Otherwise, wait for the next Windows 2000 service pack that contains this fix.

To resolve this problem immediately, download the fix by following the instructions later in this article or contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:NOTE: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

Download Information

The following file is available for download from the Microsoft Download Center:
Release Date: September 18, 2002

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base: Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.

Installation Information

You must restart your computer after you apply this update. This update supports the following Setup switches:

• /? Display the list of installation switches.
• /u Unattended mode.
• /f Force other programs to quit when the computer shuts down.
• /n Do not back up files for removal.
• /o Overwrite OEM files without prompting.
• /z Do not restart when installation is complete.
• /q Quiet mode (no user interaction).
• /l List installed hotfixes.
• /x Extracts the files without running Setup.

For example, the following command line installs the update without any user intervention and then does not force the computer to restart: WARNING: Your computer is vulnerable until you restart it.

File Information

The English version of this fix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

The following file is installed in the %Windir%\System32\Drivers folder: NOTE: Because of file dependencies, this update requires Windows 2000 Service Pack 2 (SP2) or Service Pack 3 (SP3). For additional information, click the article number below to view the article in the Microsoft Knowledge Base:

Windows XP

Microsoft has confirmed that this problem may cause a degree of security vulnerability in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Windows XP Service Pack 1 (SP1).

Windows 2000

Microsoft has confirmed that this problem may cause a degree of security vulnerability in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Microsoft Windows 2000 Service Pack 4.

For more information about this vulnerability, visit the following Microsoft Web site: