samba - Jan 2018 - Account is sensitive and cannot be delegated (userAccountControl NOT_DELEGATED flag 0x00100000)

I have an AD with two Debian Stretch Samba 4.5.12 DCs. The Samba and Heimdal
Kerberos 7.1.0 packages are installed from Debian repositories. Management is
done from MS-RSAT installed on a Windows 7 Pro client.

When I select the option "Account is sensitive and cannot be
delegated" (in Active Directory Users and Computers under the Account tab)
for a user account regardless of its privileges, the user cannot logon on any
client PC. Windows 7 responds "Logon failure: user account restriction.
Possible reasons are blank passwords are not allowed, logon hour restrictions,
or a policy restriction has been enforced" and a Debian Stretch client
responds "You are not allowed to logon from this workstation". The
Samba DC will provide a non-forwardable TGT, if you ask for it with kinit -F
command from the Linux client. Issuing the command kinit -f will again fail with
"krb5_get_init_creds: Ticket may not be forwardable".

Investigation with Wireshark showed that after receiving an AS-REQ for a TGT
with the forwardable flag set, the Samba 4.5.12 DC responds a KRB5KDC_ERR_POLICY
with e-text "Ticket may not be forwardabale" (same as kinit -f). This
behavior is correct according to CVE-2016-2125
(https://www.samba.org/samba/security/CVE-2016-2125.html) which states:

0x00100000: UF_NOT_DELEGATED:
The UF_NOT_DELEGATED can be used to disable the ability to get forwardable TGT
for the account. It means the KDC will respond with an error if the client asks
for the forwardable ticket.  The client typically gives up and removes the
GSS_C_DELEG_FLAG flag and continues without passing delegated credentials.
Administrators can use this to disable possible delegation for the most
privileged accounts (e.g. administrator accounts).

Upon the initial logon procedure however, both Samba 4.5.12 and Windows 7
clients will actually give up and not continue asking for a non-forwardable TGT,
which means that the user will be locked out.

Testing with Wireshark on another AD with one Windows 2008 R2 DC showed that the
DC ignored the forwardable flag on AS-REQ and the user logged in normally having
a non-forwardable TGT. All subsequent TGS requests on the same logon session
from a Windows 7 client didn't have the forwardable flag set.

Should I fill a bug for that, request to be added on Samba wiki or am I doing
something wrong?

Thank you in advance,
Antonios Kalkakos

FWIW same applies to a domain with DCs running on Samba 4.7.4 and Windows 7
client.
> -----Original Message-----
> From: samba [mailto:samba-bounces at lists.samba.org] On Behalf Of Antonios
> Kalkakos via samba
> Sent: 06 January 2018 11:11
> To: samba at lists.samba.org
> Subject: [Samba] Account is sensitive and cannot be delegated
> (userAccountControl NOT_DELEGATED flag 0x00100000)
> 
> I have an AD with two Debian Stretch Samba 4.5.12 DCs. The Samba and
Heimdal
> Kerberos 7.1.0 packages are installed from Debian repositories. Management
is
> done from MS-RSAT installed on a Windows 7 Pro client.
> 
> When I select the option "Account is sensitive and cannot be
delegated" (in
> Active Directory Users and Computers under the Account tab) for a user
account
> regardless of its privileges, the user cannot logon on any client PC.
Windows 7
> responds "Logon failure: user account restriction. Possible reasons
are blank
> passwords are not allowed, logon hour restrictions, or a policy restriction
has
> been enforced" and a Debian Stretch client responds "You are not
allowed to
> logon from this workstation". The Samba DC will provide a
non-forwardable TGT,
> if you ask for it with kinit -F command from the Linux client. Issuing the
command
> kinit -f will again fail with "krb5_get_init_creds: Ticket may not be
forwardable".
> 
> Investigation with Wireshark showed that after receiving an AS-REQ for a
TGT
> with the forwardable flag set, the Samba 4.5.12 DC responds a
> KRB5KDC_ERR_POLICY with e-text "Ticket may not be forwardabale"
(same as
> kinit -f). This behavior is correct according to CVE-2016-2125
> (https://www.samba.org/samba/security/CVE-2016-2125.html) which states:
> 
> 0x00100000: UF_NOT_DELEGATED:
> The UF_NOT_DELEGATED can be used to disable the ability to get forwardable
> TGT
> for the account. It means the KDC will respond with an error if the client
asks
> for the forwardable ticket.  The client typically gives up and removes the
> GSS_C_DELEG_FLAG flag and continues without passing delegated credentials.
> Administrators can use this to disable possible delegation for the most
> privileged accounts (e.g. administrator accounts).
> 
> Upon the initial logon procedure however, both Samba 4.5.12 and Windows 7
> clients will actually give up and not continue asking for a non-forwardable
TGT,
> which means that the user will be locked out.
> 
> Testing with Wireshark on another AD with one Windows 2008 R2 DC showed
> that the DC ignored the forwardable flag on AS-REQ and the user logged in
> normally having a non-forwardable TGT. All subsequent TGS requests on the
> same logon session from a Windows 7 client didn't have the forwardable
flag set.
> 
> Should I fill a bug for that, request to be added on Samba wiki or am I
doing
> something wrong?
> 
> Thank you in advance,
> Antonios Kalkakos
> --
> To unsubscribe from this list go to the following URL and read the
> instructions:  https://lists.samba.org/mailman/options/samba

On Sat, 6 Jan 2018 11:11:22 +0000
Antonios Kalkakos via samba <samba at lists.samba.org> wrote:
> I have an AD with two Debian Stretch Samba 4.5.12 DCs. The Samba and
> Heimdal Kerberos 7.1.0 packages are installed from Debian
> repositories. Management is done from MS-RSAT installed on a Windows
> 7 Pro client.
> 
What Heimdal Kerberos packages have you installed on the DCs ?

Client or Server ?

If the later, remove them, Samba ships with its own kerberos server.

Rowland

On 6/1/2018 14:29, Rowland Penny via samba wrote:
What Heimdal Kerberos packages have you installed on the DCs ?


Client or Server ?

If the later, remove them, Samba ships with its own kerberos server.

Rowland



Only the package heimdal-clients which provides the kinit, klist and kdestroy
and its dependencies. Server packages such as heimdal-kdc, heimdal-servers are
not installed.

On Sat, 2018-01-06 at 11:11 +0000, Antonios Kalkakos via samba
wrote:
> I have an AD with two Debian Stretch Samba 4.5.12 DCs. The Samba and
Heimdal Kerberos 7.1.0 packages are installed from Debian repositories.
Management is done from MS-RSAT installed on a Windows 7 Pro client.
> 
> When I select the option "Account is sensitive and cannot be
delegated" (in Active Directory Users and Computers under the Account tab)
for a user account regardless of its privileges, the user cannot logon on any
client PC. Windows 7 responds "Logon failure: user account restriction.
Possible reasons are blank passwords are not allowed, logon hour restrictions,
or a policy restriction has been enforced" and a Debian Stretch client
responds "You are not allowed to logon from this workstation". The
Samba DC will provide a non-forwardable TGT, if you ask for it with kinit -F
command from the Linux client. Issuing the command kinit -f will again fail with
"krb5_get_init_creds: Ticket may not be forwardable".
> 
> Investigation with Wireshark showed that after receiving an AS-REQ for a
TGT with the forwardable flag set, the Samba 4.5.12 DC responds a
KRB5KDC_ERR_POLICY with e-text "Ticket may not be forwardabale" (same
as kinit -f). This behavior is correct according to CVE-2016-2125
(https://www.samba.org/samba/security/CVE-2016-2125.html) which states:
> 
> 0x00100000: UF_NOT_DELEGATED:
> The UF_NOT_DELEGATED can be used to disable the ability to get forwardable
TGT
> for the account. It means the KDC will respond with an error if the client
asks
> for the forwardable ticket.  The client typically gives up and removes the
> GSS_C_DELEG_FLAG flag and continues without passing delegated credentials.
> Administrators can use this to disable possible delegation for the most
> privileged accounts (e.g. administrator accounts).
> 
> Upon the initial logon procedure however, both Samba 4.5.12 and Windows 7
clients will actually give up and not continue asking for a non-forwardable TGT,
which means that the user will be locked out.
> 
> Testing with Wireshark on another AD with one Windows 2008 R2 DC showed
that the DC ignored the forwardable flag on AS-REQ and the user logged in
normally having a non-forwardable TGT. All subsequent TGS requests on the same
logon session from a Windows 7 client didn't have the forwardable flag set.
> 
> Should I fill a bug for that, request to be added on Samba wiki or am I
doing something wrong?
Yes, please file a bug.  Clearly we need a test for this. 

(Regarding Rowland's point, the Heimdal package on Debian won't
actually be used by the Samba 4.5 package). 

Andrew Bartlett
-- 
Andrew Bartlett                       http://samba.org/~abartlet/
Authentication Developer, Samba Team  http://samba.org
Samba Developer, Catalyst IT          http://catalyst.net.nz/services/samba

On 6/1/2018 23:55, Andrew Bartlett wrote:
> On Sat, 2018-01-06 at 11:11 +0000, Antonios Kalkakos via samba wrote:
>> I have an AD with two Debian Stretch Samba 4.5.12 DCs. The Samba and
Heimdal Kerberos 7.1.0 packages are installed from Debian repositories.
Management is done from MS-RSAT installed on a Windows 7 Pro client.
>>
>> When I select the option "Account is sensitive and cannot be
delegated" (in Active Directory Users and Computers under the Account tab)
for a user account regardless of its privileges, the user cannot logon on any
client PC. Windows 7 responds "Logon failure: user account restriction.
Possible reasons are blank passwords are not allowed, logon hour restrictions,
or a policy restriction has been enforced" and a Debian Stretch client
responds "You are not allowed to logon from this workstation". The
Samba DC will provide a non-forwardable TGT, if you ask for it with kinit -F
command from the Linux client. Issuing the command kinit -f will again fail with
"krb5_get_init_creds: Ticket may not be forwardable".
>>
>> Investigation with Wireshark showed that after receiving an AS-REQ for
a TGT with the forwardable flag set, the Samba 4.5.12 DC responds a
KRB5KDC_ERR_POLICY with e-text "Ticket may not be forwardabale" (same
as kinit -f). This behavior is correct according to CVE-2016-2125
(https://www.samba.org/samba/security/CVE-2016-2125.html) which states:
>>
>> 0x00100000: UF_NOT_DELEGATED:
>> The UF_NOT_DELEGATED can be used to disable the ability to get
forwardable TGT
>> for the account. It means the KDC will respond with an error if the
client asks
>> for the forwardable ticket.  The client typically gives up and removes
the
>> GSS_C_DELEG_FLAG flag and continues without passing delegated
credentials.
>> Administrators can use this to disable possible delegation for the most
>> privileged accounts (e.g. administrator accounts).
>>
>> Upon the initial logon procedure however, both Samba 4.5.12 and Windows
7 clients will actually give up and not continue asking for a non-forwardable
TGT, which means that the user will be locked out.
>>
>> Testing with Wireshark on another AD with one Windows 2008 R2 DC showed
that the DC ignored the forwardable flag on AS-REQ and the user logged in
normally having a non-forwardable TGT. All subsequent TGS requests on the same
logon session from a Windows 7 client didn't have the forwardable flag set.
>>
>> Should I fill a bug for that, request to be added on Samba wiki or am I
doing something wrong?
> Yes, please file a bug.  Clearly we need a test for this.
>
> (Regarding Rowland's point, the Heimdal package on Debian won't
> actually be used by the Samba 4.5 package).
>
> Andrew Bartlett
I have filled Bug 13205 with a proposed patch. It also affects Samba 
versions 4.7.4 and 4.8.0rc2.