Kinit should work from any host, whether that host is part of the domain or 
not. It contains no inherent knowledge of any passwords. If it succeeds, then 
you either picked a bad password, stored the password in a plaintext file, or 
an actual authorized user ran it. It seems that it would make more sense to 
fret about how to somehow revoke any TGTs already issued to that machine.

Kinit authenticates the person running it, not the host it is running from. In 
your example, it successfully authenticated you because you know your admin 
password. If an attacker knows your admin password, focusing on your one 
compromised host is _not_ where you should be spending your energies.


-----Original Message-----
[] On Behalf Of Paessens, Daniel
Sent: Wednesday, November 16, 2016 2:58 AM
To: Martin Babinsky <>;
Subject: Re: [Freeipa-users] Actions for a stolen/compromised IPA Client

Indeed the kinit keeps working correctly.
If you give a good password it retrieves the tokens correctly.
Thus it's not only DOS, but also an potentional brutal password retriever as 
Blocking on firewall level,ok, but what if you use DHCP. It's more difficult to 
protect it, through that way.


-----Original Message-----
From: Martin Babinsky []
Sent: Wednesday, November 16, 2016 10:30 AM
To: Paessens, Daniel <>;
Subject: Re: [Freeipa-users] Actions for a stolen/compromised IPA Client

On 11/16/2016 10:04 AM, Paessens, Daniel wrote:
> Currently am I looking for a workable solution for the following situation:
>     Let's say that an ipa client has been stolen (or compromised).
> What can we do to block all access from it, towards IPA (and rest)
>     For example if we use the command "ipa host-disable" it's noticed
> that IPA users are no longer able to login into the system. But if you
> log into the system as root. Then you can still run (successfully) the
> command kinit, and optain a ticket for it.
>     Even if you delete the host from the directory, the behavior
> remains the same.
>     Can this anyhow be blocked.
>     Regards,
>     Daniel

Hi Daniel,

host-disable removes the host kerberos keys and certificates from LDAP as you 
correctly observer. This means that all services on the compromised host stop 
working. SSSD will also stop working since it uses the now invalid host keytab 
to perform user lookup, that's why ssh'ing to host as IPA user stops working.

However, there is nothing preventing the attacker to try to kinit as admin 
directly without sssd on the machine, which can potentialy lead to DoS attack 
on the admin user. So if you realize that the host was compromised it is best 
to first run hist-disable and then block all traffic from that host on ports 88 
tcp/udp (Kerberos), 464 tcp/udp (kadmin), 749 tcp/udp (kpasswd IIRC) and 
LDAP(S) ports (389, 636 tcp).

Martin^3 Babinsky

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