Question about excluding the PAC

Wed Jan 30 08:49:23 EST 2019

Thanks everyone, I will investigate the options. I know there is also a — nopac option on the kinit that I can set for the SPN but not sure if that will apply to.

Thanks again

Sent from my iPhone

> On Jan 30, 2019, at 4:21 AM, Mark Pröhl <mark at mproehl.net> wrote:
>
> Some more tips/links:
>
> (1) You should check that no others kerberized services that require
>    service tickets with a PAC are associated with the same AD account
>    as your web service. It is best practice to use a dedicated AD
>    service account only for the HTTP principal.
>
> (2) Technically you need to modify the attribute userAccounControl of
>    the AD account that is associated with the HTTP principal. This
>    attribute is a bit-mask and you need to add the value 0x02000000
>    (ADS_UF_NO_AUTH_DATA_REQUIRED). See also:
>    https://urldefense.proofpoint.com/v2/url?u=https-3A__msdn.microsoft.com_en-2Dus_library_cc223145.aspx&d=DwIDaQ&c=A-GX6P9ovB1qTBp7iQve2Q&r=9ggArrKwg0XCMk2h_JcalRiGjZ1d7o1PDuo5y6VpEPI&m=52UngoH6izxN_k8vacztJN8M-wKd6WTUfFDqsZlB01E&s=LrwfQR_dBBHJn0s3RDfGMWW58eADP-rBNVfMbQY-9as&e=.
>
> (3) IMO the easiest way to disable PAC is provided by msktutil
>    (https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_msktutil_msktutil&d=DwIDaQ&c=A-GX6P9ovB1qTBp7iQve2Q&r=9ggArrKwg0XCMk2h_JcalRiGjZ1d7o1PDuo5y6VpEPI&m=52UngoH6izxN_k8vacztJN8M-wKd6WTUfFDqsZlB01E&s=1BTHnzAv_4x44gZ12vV6jJu8-Q_oKrnXDkF6gfhW5Jc&e=).
>    Man msktutil and search for --no-pac
>
> (4) Users need to obtain new Kerberos tickets after this modification
>
> - Mark
>
>
>> On 1/30/19 12:00 PM, Simo Sorce wrote:
>> The best and only way forward for you is to ask your AD admins to
>> disable PAC for your HTTP server. Then *all* clients will get tickets
>> w/o the PAC. You cannot do anything on the HTTP server, it is too late,
>> big tickets with PACs have already been sent to you.
>>
>> Regards,
>> Simo.
>>
>>> On Tue, 2019-01-29 at 21:05 +0000, Schwartz, John wrote:
>>> The KDC is Active Directory. The problem I need to do for all logged in users and the main reason is that we do not need authorization data and we had to increase the http header size to the max to allow what we have. I fear that once a few users get added to a few more groups, it can push us over the limit.
>>>
>>> The other way to fix it is if there was good group management but with around 70K users, that would be nearly impossible to remediate.
>>>
>>> No one needs to be a part of a couple of hundred or more groups.
>>>
>>> Kerberos provides documentation to code API's and reference them from the krb5.conf but (at least for me) it is not clear enough of how to integrate.
>>>
>>> They provider the variable that needs to be modified but do not say which header file it belongs to etc...
>>>
>>> Thanks,
>>>
>>> Anthem, Inc.
>>>
>>> John Schwartz,  Exec Advisor, Authentication Services
>>> 21555 Oxnard St., Woodland Hills, California 91367
>>> O: (818) 234-6763 |
>>> john.schwartz at anthem.com
>>>
>>>
>>> -----Original Message-----
>>> From: Mark Pröhl [mailto:mark at mproehl.net]
>>> Sent: Tuesday, January 29, 2019 12:59 PM
>>> To: Schwartz, John <John.Schwartz at anthem.com>; krbdev at mit.edu
>>> Subject: Re: Question about excluding the PAC
>>>
>>> Hi,
>>>
>>> I wonder what kind of Kerberos infrastructure is providing the PAC. In case of Active Directory you typically can get rid of the pac by modifying the service account that is associated with the HTTP principal. This only affects tickets for that particular service.
>>> Maybe your implementation on Linux offers a similar way?
>>>
>>> Regards,
>>>
>>> Mark Pröhl
>>>
>>>> On 1/25/19 10:56 PM, Schwartz, John wrote:
>>>> All, I have a Kerberos 5 implementation running on Linux and is integrated with the web server for website SSO access.
>>>>
>>>> I have a need to exclude the PAC from the request ticket and am looking for the simplest way to do that.
>>>>
>>>> I see that kinit has the option "--no-request-pac"
>>>>
>>>> Is there a similar way to do it from the krb5.conf or does it need a custom shared object?
>>>>
>>>> If it needs a custom shared object, can someone provide sample code?  I am not able to tell from the existing documentation what needs to be done.
>>>>
>>>> Any assistance is greatly appreciated.
>>>>
>>>> Thank you,
>>>>
>>>> Anthem, Inc.
>>>>
>>>>
>>>>
>>>> John Schwartz,  Exec Advisor, Authentication Services
>>>> 21555 Oxnard St., Woodland Hills, California 91367
>>>> O: (818) 234-6763 |
>>>> john.schwartz at anthem.com
>>>>
>>>>
>>>>
>>>>
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>>
>

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