[BUG] JGSS is querying wrong realm for service ticket and fails ultimately

[Wei-Jun Wang]

Hi Michael,

Java starts from the default KDC and it expects a referral could happen. Does MIT krb5 always start from the client’s own KDC?

If you change the default realm to AD001.SIEMENS.NET<http://AD001.SIEMENS.NET>, does it work? Does it work with your other scenarios?

Thanks,
Max

On Aug 30, 2024, at 05:09, Osipov, Michael (IN IT IN) <michael.osipov at innomotics.com> wrote:

Folks,

please consider the following case/bug with JGSS:
Tried with OpenJDK 8u4xx, can try newer, but doubt that it will be any different.

* KDCs are Active Directory
* Machine: member of INNOMOTICS.NET
* krb5.conf: Default realm is INNOMOTICS.NET
* Client: Logged in from a different realm in this machine: foo at AD001.SIEMENS.NET
* One-way trust from AD001.SIEMENS.NET, means with an account from AD001.SIEMENS.NET you can access resources from both realms, but you cannot access resources from AD001.SIEMENS.NET with your INNOMOTICS.NET account. That is on purpose.

Use case:
Client wants to access AD DS via LDAP and authenticate with an SASL GSSAPI bind: ldap at dc1.ad001.siemens.net. Client and target realm are identical. AS-REQ, AS-REP from AD001.SIEMENS.NET are fine, now here is the problem: To form the TGS-REQ it requests a cross-realm TGT for INNOMOTICS.NET and then asks a KDC in INNOMOTICS.NET for a service ticket for ldap at dc1.ad001.siemens.net. This KDC of course says:
16174 >>>KRBError:
16175      sTime is Thu Aug 29 20:19:07 CEST 2024 1724955547000
16176      suSec is 106542
16177      error code is 7
16178      error Message is Server not found in Kerberos database
16179      sname is ldap/dc1.ad001.siemens.net at INNOMOTICS.NET
16180      msgType is 30

End of story. The bug for me is that, for some reason, JGSS assumes that the target is in the default realm of the machine instead of asking its own realm which should give it all necessary cross-realm referrals.

Here is what MIT Kerberos does:
$ cat /etc/krb5.conf
# Kerberos configuration
[libdefaults]
   default_realm = INNOMOTICS.NET
   forwardable = true
   canonicalize = true
   dns_lookup_kdc = true
   dns_canonicalize_hostname = false
   qualify_shortname = ""
   rdns = false
   udp_preference_limit = 1
   kdc_timeout = 1000
   max_retries = 1
$ klist
Ticketzwischenspeicher: FILE:/tmp/krb5cc_2011
Standard-Principal: foo at AD001.SIEMENS.NET
Valid starting       Expires              Service principal
2024-08-30T10:13:05  2024-08-30T20:13:05  krbtgt/AD001.SIEMENS.NET at AD001.SIEMENS.NET
       erneuern bis 2024-08-31T10:10:22
$ ldapwhoami -H ldap://ad001.siemens.net
SASL/GSSAPI authentication started
SASL username: foo at AD001.SIEMENS.NET
SASL SSF: 256
SASL data security layer installed.
u:AD001\foo
$ klist
Ticketzwischenspeicher: FILE:/tmp/krb5cc_2011
Standard-Principal: foo at AD001.SIEMENS.NET
Valid starting       Expires              Service principal
2024-08-30T10:13:05  2024-08-30T20:13:05  krbtgt/AD001.SIEMENS.NET at AD001.SIEMENS.NET
       erneuern bis 2024-08-31T10:10:22
2024-08-30T10:13:19  2024-08-30T20:13:05  ldap/dc1.ad001.siemens.net@
       erneuern bis 2024-08-31T10:10:22
       Ticket server: ldap/dc1.ad001.siemens.net at AD001.SIEMENS.NET

Also looking at the output of KRB5_TRACE and pcaps MIT Kerberos never contacts any KDC in INNOMOTICS.NET.

The workaround is the following in krb5.conf:
# JGSS does not use the client's realm to obtain a ticket and needs this hinT
[domain_realm]
   .ad001.siemens.net = AD001.SIEMENS.NET
   ad001.siemens.net = AD001.SIEMENS.NET

This is ugly because:
* I have to do this on all affected machines and cannot rely on AD to give me the right referral
* if I have an SPN, e.g. HTTP/svc.ad001.siemens.net in INNOMOTICS.NET, a migrated machine from AD001.SIEMENS.NET to INNOMOTICS.NET available under multiple virtual hostnames the init_sec_context will likely fail because that SPN is not known AD001.SIEMENS.NET, I can hope that AD will send me a referral. But in any case it will incur unnecessary round trips. I need to explicitly exempt those hosts here throughout my setup.

Max, can you have a look at this? I can provide all the necessary debug/trace/pcap files to you. Just let me know what you would like to see.

Michael

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