Query regarding S4U2Self protocol extension

Isaac Boukris iboukris at gmail.com
Tue Jul 27 06:17:07 EDT 2021

On Mon, Jul 26, 2021 at 10:17 PM Greg Hudson <ghudson at mit.edu> wrote:
> On 7/23/21 4:38 PM, Vipul Mehta wrote:
> > I did some testing with Windows KDC and it will set forwardable flag in
> > S4U2Self service ticket in either of the following cases:
> >
> > 1) TrustedToAuthForDelegation is set to true in Service A account.
> >
> > 2) Service A TGT used in S4U2Self has forwardable flag set and
> > msDS-AllowedToDelegateTo list is empty on Service A account.
> > I am not able to understand why msDS-AllowedToDelegateTo needs to be empty
> > in the 2nd case.
> >
> > Is the behavior of MIT KDC the same as Windows KDC ?
> We have an analog of the TrustedToAuthForDelegation flag, called
> ok_to_auth_as_delegate.  We don't check for an empty
> allowed-to-delegate-to list.
> https://support.microsoft.com/en-us/topic/managing-deployment-of-rbcd-protected-user-changes-for-cve-2020-16996-9a59a49f-20b9-a292-f205-da9da0ff24d3

Now that I read this again, and read again the "Additional
considerations" section in that link, I think what might happened with
this change is that now RBCD requires the forwardable flag but any
service with an empty msDS-AllowedToDelegateTo to list, as Vipul
remarked, gets treated as TrustedToAuthForDelegation and gets the flag
(presumably, unless the client is in the protected-users group or has
the not-delegated flag).

I'll run some tests and check it with dochelp.

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