[Samba] Remote Desktop problem on samba 4.17.2

[Matthew Schumacher]

On 10/27/22 4:36 PM, Matthew Schumacher via samba wrote:
>
> I'm also having problems with RDP sessions not authenticating against 
> samba heimdal kdc.  What is odd is that the initial RDP connection 
> (network level connection) works fine and authenticates me, but when I 
> get to the desktop, I get access denied and that my password is wrong 
> as if I used a wrong password at the console. If I put in the wrong 
> password into the initial rdp session for network level connection, it 
> immediately rejects me without letting me see the desktop.
>
> Looking at wireshark under the covers, I suspect it's a kerberos 
> issue, however all of my hosts have dns settings of samba domain 
> controllers and my samba servers do appear to get AD updates.
>
> I was running 4.16.4 but now I'm on 4.17.2 with no change.
>
> I wonder if something changed on the windows side.   I see Jakob 
> posted about a 22H2 update breaking this.  Anyone know the specific 
> fix and how to roll it back?
>

Looking at this more, the 22H2 issue doesn't seem to be the same issue 
I'm dealing with as Ralph and others mentioned that it goes away when 
they upgrade to latest (which I'm on), also I'm not seeing the 
KRB5KDC_ERR_TGT_REVOKED error.

Here is what I found in regard to my issue:

If I have a windows host with RDP authenticate against samba AD it 
starts an RDP session, but then rejects the password when we get the 
desktop.  Looking at the packet captures I see:

This part looks identical other than keys between the captures that work 
against a real windows dc and captures that don't work against a SAMBA DC:

 From client: as-req
 From server: KRB5KDC_ERR_PREAUTH_REQUIRED
 From client: as-req

Now that we get to the as-rep we start to see differences:

 From Windows: as-rep->ticket->enc-part->etype 
eTYPE-ARCFOUR-HMAC-MD5(23)    and    ap-rep->enc-part->etype 
eTYPE-AES256-CTS-HMAC-SHA1-96(18)
 From Samba: 
as-rep->ticket->enc-part->etype eTYPE-AES256-CTS-HMAC-SHA1-96(18)   
and    ap-rep->enc-part->etype eTYPE-AES256-CTS-HMAC-SHA1-96(18)

Then we see the TGS-REQ and the client asks for a 
eTYPE-AES256-CTS-HMAC-SHA1-96(18) from the samba AD and 
eTYPE-ARCFOUR-HMAC-MD5(23) from the windows server otherwise identical.

Now the TGS-REP

 From Windows: tgs-rep->ticket->enc-part->etype 
eTYPE-ARCFOUR-HMAC-MD5(23)    and    tgs-rep->enc-part->etype 
eTYPE-ARCFOUR-HMAC-MD5(23)
 From Samba: 
tgs-rep->ticket->enc-part->etype eTYPE-AES256-CTS-HMAC-SHA1-96(18)   
and    tgs-rep->enc-part->etype eTYPE-AES256-CTS-HMAC-SHA1-96(18)

Basically, it appears that windows is using MD5 hashing and samba SHA1.

A this point there aren't any further kerberos interactions from the 
client when authenticating to samba and the desktop shows password 
failed.  When using the windows AD server we get another TGS-REQ/TGS-REP 
for sname kRB5-NT-SRV-INST where it appears to authenticate for LDAP.

So, where to go from here?  Create a Heimdal bug?  Create a Samba bug?  
Not having RDP is really causing issues for me.

Thanks,
Matt