[cifs-protocol] [EXTERNAL] Windows Server 2025 PKINIT regression - TrackingID#2412190040009154

[Michael Bowen]

Hi Julien,

Thanks for the update. @Kristian Smith is handling your case, so I'm forwarding this to him to help him with your issue. Happy Holidays!

- Michael

-----Original Message-----
From: Julien Rische <jrische at redhat.com> 
Sent: Monday, December 23, 2024 5:32 AM
To: Michael Bowen <Mike.Bowen at microsoft.com>
Cc: Alexander Bokovoy <ab at samba.org>; cifs-protocol at lists.samba.org; Microsoft Support <supportmail at microsoft.com>
Subject: Re: [cifs-protocol] [EXTERNAL] Windows Server 2025 PKINIT regression - TrackingID#2412190040009154

[You don't often get email from jrische at redhat.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]

Hello Michael,

It has come to our attention that Windows Server 2025 now has support for allowing and disallowing digest algorithms in PKINIT. We made some tests by modifying the "Computer Configuration\Policies\Administrative
Templates\System\KDC\Configure hash algorithms for certificate logon".

This configuration seems to take effect, because disallowing SHA-256 causes elliptic curve Diffie-Hellman to fail. However, allowing all SHA versions does not fix the problem when using finite field Diffie-Hellman.

In attachment, you will find 2 network traces showing a successful pre-authentication process for ECDH with curve P-256 and RSA/SHA-256 signature, and a failing one for FFDH with MODP group 14 (2046-bit) and RSA/SHA-256 signature. In both cases all SHA versions are allowed in the above group policy.

--
Julien Rische


On Thu, Dec 19, 2024 at 5:33 PM Michael Bowen via cifs-protocol <cifs-protocol at lists.samba.org> wrote:
>
> [DocHelp to bcc]
>
> Hi Alexander,
>
> Thanks for your question about Windows Server 2025 and Kerberos. I've created case number 2412190040009154 to track this issue, please leave the number in the subject line when communicating with our team. One of our engineers will contact you soon.
>
> Best regards,
> Michael Bowen
> Sr. Escalation Engineer - Microsoft® Corporation
>
> -----Original Message-----
> From: Alexander Bokovoy <ab at samba.org>
> Sent: Thursday, December 19, 2024 4:26 AM
> To: Interoperability Documentation Help <dochelp at microsoft.com>
> Cc: cifs-protocol at lists.samba.org
> Subject: [EXTERNAL] Windows Server 2025 PKINIT regression
>
> [Some people who received this message don't often get email from 
> ab at samba.org. Learn why this is important at 
> https://aka.ms/LearnAboutSenderIdentification ]
>
> Hi Dochelp,
>
> I believe we are seeing a regression in how Windows Server 2025 handles Kerberos PKINIT, probably due to algorithm agility rewrite.
>
> Sometime ago we have updated MIT Kerberos implementation of PKINIT to use sha256WithRSAEncryption in supported CMS types and removed sha1WithRSAEncryption to be able compliant with FIPS 140-3.
>
> The commit 
> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgith
> ub.com%2Fkrb5%2Fkrb5%2Fcommit%2Fcbfe46ce20f3e9265baa9c648390148c739ab8
> 30&data=05%7C02%7Cmike.bowen%40microsoft.com%7C6c48431e145e4de8500c08d
> d23562d38%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C638705575372721
> 071%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMC
> IsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=
> BKt0Ke6K6mn1ONoQTBrHhhybs8HASTsXpFQC4qPKjKo%3D&reserved=0
> is part of MIT Kerberos 1.20 or later releases.
>
> This change worked well for Windows Server versions prior to Windows Server 2025 release. With Windows Server 2025, the request is rejected (packet 8 from ad2025.pcap in attached archive):
>
> Kerberos
>     Record Mark: 106 bytes
>         0... .... .... .... .... .... .... .... = Reserved: Not set
>         .000 0000 0000 0000 0000 0000 0110 1010 = Record Length: 106
>     krb-error
>         pvno: 5
>         msg-type: krb-error (30)
>         stime: Dec 18, 2024 15:22:36.000000000 CET
>         susec: 926640
>         error-code: Unknown (79)
>         realm: WIN2025-UO83.TEST
>         sname
>             name-type: kRB5-NT-SRV-INST (2)
>             sname-string: 2 items
>                 SNameString: krbtgt
>                 SNameString: WIN2025-UO83.TEST
>
>
> We built a custom version of MIT Kerberos which adds both sha256WithRSAEncryption and sha1WithRSAEncryption to the list of supported CMS types and still signed with sha256WithRSAEncryption, it failed again. The corresponding packet exchange can be seen in ad2025_sha1.pcap in the attached archive.
>
> Both variants work against Windows Server 2019, so to us this looks like a regression in Windows Server 2025 implementation.
>
> If this is not a regression and instead it is an intentional change, could you please make sure MS-PKCA and other corresponding documents get updated with a proper logic of the changes.
>
> --
> / Alexander Bokovoy
>
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