A remote code execution vulnerability exists in the Credential Security Support Provider protocol (CredSSP). An attacker who successfully exploited this vulnerability could relay user credentials and use them to execute code on the target system. CredSSP is an authentication provider which processes authentication requests for other applications; any application which depends on CredSSP for authentication may be vulnerable to this type of attack. As an example of how an attacker could exploit this vulnerability against Remote Desktop Protocol, the attacker would need to run a specially crafted application and perform a man-in-the-middle attack against a Remote Desktop Protocol session. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. The security update addresses the vulnerability by correcting how Credential Security Support Provider protocol (CredSSP) validates requests during the authentication process.
The vulnerability impacts Windows 7, Windows 8.1, and Windows 10 systems, as well as Windows Server 2008, Windows Server 2012, and Windows Server 2016.
Download patches here
To address the issue, Microsoft released an update to correct the manner in which CredSSP validates requests during the authentication process. The update patches the CredSSP authentication protocol and the Remote Desktop clients for all affected platforms.
“Mitigation consists of installing the update on all client and server operating systems and then using included Group Policy settings or registry-based equivalents to manage the setting options on the client and server computers. We recommend that administrators apply the policy and set it to “Force updated clients” or “Mitigated” on client and server computers as soon as possible,” Microsoft says.
I have noticed that this patch has been disruptive to system owners who use remote desktop to access and manage servers. Installing the patch on a client host w/o having it installed on the remote endpoint will end in an error preventing you from accessing them.
Its best to upgrade endpoints (servers) before client systems