RDP Error: CredSSP Encryption Oracle Remediation

Kerry Tyler explains an error message popping up in RDP sessions:

In March, a vulnerability in CredSSP (Credential Security Support Provider) was patched, which would affect authentication via RDP (this is outlined in advisory CVE-2018-0886).  However, it was implemented in such a way that the behavior change didn’t have to be “honored” by either the server or the client involved in an RDP session.

The intent was that this would be controlled by GPO in enterprise environments, and a new GPO setting to activate or deactivate this behavior was released at the same time.

GPO settings have a default value, which they will use when nothing has been explicitly set for a particular setting. In this case, the GPO has three possible values: Force Updated Clients (for servers to only take connections from patched clients), Mitigated (for both, and on a workstation means that it won’t fall back to old/insecure behavior when attaching to unpatched servers), and Vulnerable (for both, and means what it sounds like–anything goes!).

In March, the default behavior was set to “Vulnerable”, which means everything kept working for everyone. But in the May security rollup, the default setting for that GPO was flipped to “Mitigated” if there was not an explicit setting for it…

If you get this error, the best thing is to patch the machines involved, but Kerry shows the workaround you can use if you need to use RDP in the meantime to connect to an unpatched machine.

Related Posts

Operating Management Studio With Multiple Active Directory Accounts

Kenneth Fisher shows how to use different Active Directory credentials when using SQL Server Management Studio: To help promote the seperation of duties one of the things my company has done is to divide our permissions into two accounts. We have one account that is for our daily tasks. Reading email, searching the internet, basic […]

Read More

More dbatools Changes

Chrissy LeMaire has a few more breaking changes for us: It’s been a busy couple days! Here’s a list of our breaking changes Invoke-Sqlcmd2 has been removed and replaced with a warning to use Invoke-DbaQuery The NetworkShare parameter has been renamed to SharedPath UseLastBackups has been renamed to UseLastBackup There are also several new commands […]

Read More

Categories

May 2018
MTWTFSS
« Apr Jun »
 123456
78910111213
14151617181920
21222324252627
28293031