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Credential Security Support Provider protocol CredSSP is an authentication provider that processes authentication requests for other applications. A remote code execution vulnerability exists in unpatched versions of CredSSP. An attacker who successfully exploits this vulnerability could relay user credentials to execute code on the target system.
Any application that depends on CredSSP for authentication may be vulnerable to this type of attack. This security update addresses the vulnerability by correcting how CredSSP validates requests during the authentication process. To learn more about the vulnerability, see CVE The initial March 13, , release updates the CredSSP authentication protocol and the Remote Desktop clients for all affected platforms.
Mitigation consists of installing the update on all eligible 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.
These changes will require a reboot of the affected systems. The Remote Desktop Client RDP update update in KB will enhance the error message that is presented when an updated client fails to connect to a server that has not been updated.
An update to change the default setting from Vulnerable to Mitigated. By default, after this update is installed, patched clients cannot communicate with unpatched servers. Some versions of the CredSSP protocol are vulnerable to an encryption oracle attack against the client. This policy controls compatibility with vulnerable clients and servers. This policy allows you to set the level of protection that you want for the encryption oracle vulnerability.
If you enable this policy setting, CredSSP version support will be selected based on the following options:.
Note This setting should not be deployed until all remote hosts support the newest version. Vulnerable — Client applications that use CredSSP will expose the remote servers to attacks by supporting fallback to insecure versions, and services that use CredSSP will accept unpatched clients.
The Encryption Oracle Remediation Group Policy supports the following three options, which should be applied to clients and servers:. Client applications that use CredSSP will not be able to fall back to insecure versions. Services using CredSSP will not accept unpatched clients. Client applications that use CredSSP will expose remote servers to attacks by supporting fallback to insecure versions. Note Any change to Encryption Oracle Remediation requires a reboot. Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method.
These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk. Both the client and server need to be updated, or Windows and third-party CredSSP clients may not be able to connect to Windows or third-party hosts.
See the following interoperability matrix for scenarios that are either vulnerable to the exploit or cause operational failures. Note When connecting to a Windows Remote Desktop server, the server can be configured to use a fallback mechanism that employs the TLS protocol for authentication, and users may get different results than described in this matrix. This matrix only describes the behavior of the CredSSP protocol. Event ID will be logged on patched Windows clients if the client and remote host are configured in a blocked configuration.
Unpatched pre-Windows 8. All third-party clients or servers must use the latest version of the CredSSP protocol. Please contact the vendors to determine if their software is compatible with the latest CredSSP protocol. The protocol updates can be found on the Windows Protocol Documentation site. The credssp. For more information please review the relevant articles for file version information. Need more help? Expand your skills. Get new features first. A subscription to make the most of your time.
Try one month free. Was this information helpful? Yes No. Any other feedback? The more you tell us, the more we can help. How can we improve? Send No thanks. Thank you for your feedback! Policy path and setting name. If you enable this policy setting, CredSSP version support will be selected based on the following options: Force Updated Clients — Client applications that use CredSSP will not be able to fall back to insecure versions, and services that use CredSSP will not accept unpatched clients.
Policy setting. Registry value. Client behavior. Server behavior. Services that use CredSSP will accept unpatched clients. Force updated clients. Client setting.
CVE patch status. An authentication error has occurred. The token supplied to the function is invalid. The function requested is not supported.
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