[29987] in Kerberos
Proposal to change the meaning of -allow_tix +allow_svr aka
daemon@ATHENA.MIT.EDU (Jeffrey Altman)
Wed Jun 18 16:33:09 2008
X-Envelope-From: jaltman@secure-endpoints.com
Message-ID: <485970FD.9010109@secure-endpoints.com>
Date: Wed, 18 Jun 2008 16:33:01 -0400
From: Jeffrey Altman <jaltman@secure-endpoints.com>
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"'krbdev@mit.edu'" <krbdev@mit.edu>
Reply-To: jaltman@secure-endpoints.com
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I apologize for the cross-posting but I believe that in order for this=20
proposal
receive adequate feedback that it must be discussed among both the MIT=20
Kerberos
administrator and MIT Kerberos Developer communities.
In the current implementation of the MIT KDC there are two principal poli=
cy
flags that interact in what I believe is an undesirable way when applied =
to
service principals. Copying from the Kerberos v5 System Administrator's =
Guide:
*{-|+}allow_svr*
The =E2=80=9C-allow_svr=E2=80=9D flag prohibits the issuance of servi=
ce tickets for
this principal. =E2=80=9C+allow_svr=E2=80=9D clears this flag. In eff=
ect, =E2=80=9C-allow_svr=E2=80=9D
sets the KRB5_KDB_DISALLOW_SVR flag on the principal in the database.=
=20
*{-|+}allow_tix*
The =E2=80=9C-allow_tix=E2=80=9D option forbids the issuance of any t=
ickets for this
principal. =E2=80=9C+allow_tix=E2=80=9D clears this flag. The default=
is =E2=80=9C+allow_tix=E2=80=9D.
In effect, =E2=80=9C-allow_tix=E2=80=9D sets the KRB5_KDB_DISALLOW_AL=
L_TIX flag on
the principal in the database.=20
When a TGS or AS request is received by the KDC, under the current=20
implementation the
KDC will examine the client principal to determine whether or not=20
+allow_tix is set.=20
If not, it will reject the request.
It also naturally checks the service principal to determine whether or=20
not +allow_svr is set.
If not, it will reject the request.
However, the KDC will also check the service principal to determine it=20
it is +allow_tix
or not. If it is not, then the KDC will also reject the request.
I believe that the meaning of allow_tix should be altered such that it=20
only applies to the client
in a TGS or AS request. This would permit -allow_tix to be applied to a =
service principal
and ensure that no client ticket requests can be satisfied for that=20
service principal while at
the same time permitting other principals to obtain service tickets.=20
Organizations that wish to disable the issuance of service tickets for=20
the service principal
would apply -allow_svr to the principal in addition to -allow_tix.
I believe that making this change would permit a more robust security=20
policy to be applied
to service principals without requiring the additional of new flags that =
would have overlapping
and conflicting meaning with the existing flags.
Let the discussion begin.
Jeffrey Altman
Secure Endpoints Inc.
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