Configuring RDS Clipboard Redirection settings is a basic step towards achieving a hardened server. Server hardening can be a painful procedure. If you’re reading this article, you probably already know it. Endless hours, labor, and money are invested in this process, which can often result in production breakdown despite the effort to prevent it. This article aims to provide some basic information regarding the Clipboard Redirection setting, which enables the copy pat function in remote desktop. Once you’ll decide this setting’s desired value, make sure you test it, to fully understand what will be its impact on your production. This is highly important since you don’t want it to result in damage to production.
In this article you’ll learn:
- What is Clipboard Redirection – remote desktop copy past
- The potential vulnerability in Clipboard Redirection
- How to mitigate Clipboard Redirection vulnerability
- The potential impact of changing Clipboard Redirection configuration on your network’s function
- The severity of Clipboard Redirection vulnerability
- What we recommend to configure Clipboard Redirection
- How to disable Clipboard Redirection in the most secure fashion
What is Clipboard Redirection:
The “Do not allow Clipboard redirection” setting specifies whether to prevent the sharing of clipboard contents (clipboard redirection) between a remote computer and a client computer during a Remote Desktop Services session. By disabling this setting you won’t be able to initiate a copy – past action in a remote desktop session.
You can use this setting to prevent users from redirecting clipboard data to and from the remote computer and the local computer.
*If the status is set to Enabled, users cannot redirect clipboard data.
*When Disabled, Remote Desktop Services always allows clipboard redirection (this is the default behavior).
*If the status is set to Not Configured, clipboard redirection is not specified at the Group Policy level. However, an administrator can still disable clipboard redirection using the Remote Desktop Session Host Configuration tool.
Clipboard Redirection Potential Vulnerability:
Microsoft’s clipboard sharing channel supports several data formats such as CF_HDROP, which is responsible for the “Copy & Paste” feature. When used, it allows us to simply copy a group of files from one computer to the other. If the client itself fails to prevent malicious files from entering his computer via this feature, he could be vulnerable to a path traversal attack. The server can then drop malicious files in arbitrary paths on the client’s computer. In other words, the client’s approval of the files is the only thing protecting him from this vulnerability. Considering the fact that the client doesn’t even need to verify the received files coming from the RDP server, it is almost impossible to detect the attack.
How to Mitigate Clipboard Redirection Vulnerability:
attackers commonly use RDP for malicious activity, therefore it is recommended to configure the Remote Desktop Server to only allow required tasks. If you’ve decided that some users do need the clipboard function enabled, it is recommended to segment the LANs that have RDP clipboard enabled, so they can be tracked.
The Potential Impact of Clipboard Redirection Disabling:
As simple as it sounds, remote users won’t be able to use the clipboard functionality. That may lead to damage in production for applications that rely on this ability.
CalCom’s RECOMMENDED VALUE:
HOW TO CONFIGURE Clipboard Redirection:
Windows 2016 server:
In Windows 2016, these settings are controlled within Group Policy.
- Launch “msc“.
- Navigate to “Computer Configuration” > “Administrative Templates” > “Windows Components” > “Remote Desktop Services” > “Remote Desktop Session Host“.
- Ensure “Do not allow Clipboard redirection” is set to “Enabled“.
Windows 2012 server:
- Open “Server Manager“.
- Select “Remote Desktop” Services.
- Select “Collections“.
- Select “Tasks“, then choose “Edit Properties“.
- Under the “Client Settings” tab, ensure the “Clipboard” and “Drive” are disabled.
Windows 2008 server:
- Launch “Remote Desktop Session Host Configuration” from the server.
- Under “Connections“, right-click the connection and select “Properties“.
- Select the “Client Settings” tab, and make sure the “Clipboard” box is checked. If you don’t want to allow copying and pasting of files, make sure the Drive selection is checked. Click OK when done.
Server Hardening Automation:
Since the testing process is complex and highly prove to human mistakes, we recommend automating the entire hardening process. CalCom offers a fully automated server hardening tool – CHS. CHS’s unique ability to ‘learn’ your network eliminates the need to perform lab testing while ensuring zero outages to your production environment. CHS will allow you to implement your policy directly on your production servers, hassle-free.