Windows 10 update problem: We're fixing Kerberos authentication bug, says Microsoft

Microsoft is operating on a repair for a malicious program in remaining week’s patch for a bypass vulnerability within the Kerberos Key Distribution Heart (KDC) safety characteristic. 

Microsoft has flagged the problem affecting methods that experience put in the patch for the malicious program CVE-2020-17049, probably the most 112 vulnerabilities addressed within the November 2020 Patch Tuesday replace. 

Kerberos is a client-server authentication protocol used on a couple of working methods, together with Home windows. Microsoft tried to mend a bypass within the Kerberos KDC, a characteristic that handles tickets for encrypting messages between a server and Jstomer.     

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“After putting in KB4586786 on area controllers (DCs) and read-only area controllers (RODCs) on your surroundings, chances are you’ll come across Kerberos authentication problems,” Microsoft notes in its identified problems web page for all supported model of Home windows 10.  

“That is led to via a subject in how CVE-2020-17049 used to be addressed in those updates.”

The buggy patch solely impacts Home windows Servers, Home windows 10 gadgets and programs in endeavor environments, consistent with Microsoft. 

Microsoft addressed the vulnerability via converting how the KDC validates provider tickets used with the Kerberos Constrained Delegation (KCD) as a result of there used to be a bypass factor in the best way KDC determines if a provider token can be utilized for KCD delegation.

Microsoft explains there are 3 registry surroundings values – zero, 1, and a pair of – for PerformTicketSignature to keep an eye on it, however admins would possibly come across other problems with each and every surroundings. 

“Surroundings the worth to zero would possibly purpose authentication problems when the use of S4U eventualities, comparable to scheduled duties, clustering, and services and products as an example line-of-business programs,” Microsoft states. 

Moreover, the default worth surroundings of one would possibly purpose non-Home windows purchasers authenticating to Home windows Domain names the use of Kerberos to revel in authentication problems. 

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With that surroundings, admins may just additionally see screw ups in “cross-realm referrals” on Home windows and non-Home windows gadgets for Kerberos referral tickets passing thru DCs that have not were given the Patch Tuesday replace. 

“We’re running on a answer and can supply an replace once additional information is to be had,” Microsoft notes. 

Microsoft has additionally revised its steering for deploying the replace. It has really useful admins find the KDC registry subkey, and if it exists at the device, make sure that it’s set to at least one. Then admins wish to whole the deployment to all DCs – and Learn-Handiest DCs.

“Be aware that following our unique steering of the use of the zero surroundings may just purpose identified problems with the S4USelf characteristic of Kerberos. We’re running to deal with this identified factor,” it says. 

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