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Microsoft Netlogon: Potential Upcoming Impacts of CVE-2022-38023

Published: 2023-04-08. Last Updated: 2023-04-08 05:34:20 UTC
by Xavier Mertens (Version: 1)
1 comment(s)

This has been brought to our attention by a reader (thank you, William!). The vulnerability CVE-2022-38038 affected the Microsoft Netlogon[1] procedure with an RPC escalation of privilege vulnerability. Microsoft provided a patch to fix it. It improves the Netlogon security by enforcing RPC sealing instead of signing off the communication with the Domain Controller. RPC sealing is a security measure that both signs and encrypts the messages sent over the wire by the Netlogon protocol. Microsoft released a knowledge base article[2] with more information about the technique used to fix the vulnerability.

Sealing is controlled via a registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters

"RequireSeal" can be set to the following values:

  • 0 - Disabled
  • 1 - Compatibility mode. Windows domain controllers will require that Netlogon clients use RPC Seal if they are running Windows or acting as either domain controllers or Trust accounts.
  • 2 - Enforcement mode. All clients must use RPC Seal unless they are added to the "Domain Controller: Allow vulnerable Netlogon secure channel connections" group policy object (GPO).

When the patch was released, it was in compatibility mode, but Microsoft defined an interesting timeline:

  • Nov 8, 2022: Initial deployment phase but no impact of the sealing is not present, and the possibility of disabling the Sealing
  • Dev 13, 2022: System in audit mode and events are generated (Source: Microsoft-Windows-Kerberos-Key-Distribution-Center and event IDs 43 or 44)
  • Apr 11, 2023: Initial enforcement phase, sealing can’t be disabled in the registry (Must be 1 or 2)
  • Jul 11, 2023: Authentication will fail if Sealing is not present

Many devices use Netlogon across networks. Think about NAS, multi-function printers (MFP), etc. Some vendors have already published support articles about the potential effect of this enforcement[3].

[1] https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-nrpc/ff8f970f-3e37-40f7-bd4b-af7336e4792f
[2] KB5021130: How to manage the Netlogon protocol changes related to CVE-2022-38023 - Microsoft Support
[3] https://kb.netapp.com/onprem/ontap/da/NAS/Does_CVE-2022-38023_have_any_impact_to_ONTAP_9

Xavier Mertens (@xme)
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Senior ISC Handler - Freelance Cyber Security Consultant
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1 comment(s)
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Comments

I am so confused by the 3 patches released 8 nov 2022. They all mix together.

You write EventID that corresponds to KrbtgtFullPacSignature.
For this RequireSeal it is other Events
And you write the wrong Event log, that event log is even Disabled by default.


After enabling Audit mode, you may encounter warnings in the System log on Domain Controller with Event ID 43 with source Kdcsvc to indicate Full PAC signature failures:

The Key Distribution Center (KDC) encountered a ticket that it could not validate the full PAC Signature.
See https://go.microsoft.com/fwlink/?linkid=2210019 to learn more.

After enabling Audit mode, you may encounter warnings in the System log on Domain Controller with Event ID 44 with source Kdcsvc to indicate missing Full PAC signatures:

The Key Distribution Center (KDC) encountered a ticket that did not contained the full PAC Signature.
See https://go.microsoft.com/fwlink/?linkid=2210019 to learn more.

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