Java ignores/errors canonicalized principals (NT-PRINCIPAL) from Active Directory

Osipov, Michael (LDA IT PLM) michael.osipov at siemens.com
Wed Oct 20 08:03:37 UTC 2021


Hi folks,

we have recently noticed the following with Java's kinit (tested with 
Zulu 8 and 13, code is identical in 18 as well):

> C:\Users\osipovmi>kinit osipovmi at ad001.siemens.net

I have intentionally written the realm in lowercase to rely on 
canonicalization of the AD KDC. krb5.conf contains "canonicalize = true" 
as well.

Wireshark shows me in the AS-REQ:
as-req/req-body/sname: name-type KRB5-NT-SRV-INST (2), sname-string (2): 
krbtgt and ad001.siemens.net

AS-REP:
as-rep/ticket/sname: name-type KRB5-NT-SRV-INST (2), sname-string (2): 
krbtgt and AD001.SIEMENS.NET

Hence, the KDC has properly canonicalized the sname. Java gives me:

> Exception: krb_error 41 Message stream modified (41) Message stream modified
> KrbException: Message stream modified (41)
>         at sun.security.krb5.KrbKdcRep.check(KrbKdcRep.java:55)
>         at sun.security.krb5.KrbAsRep.decrypt(KrbAsRep.java:159)
>         at sun.security.krb5.KrbAsRep.decryptUsingPassword(KrbAsRep.java:139)
>         at sun.security.krb5.KrbAsReqBuilder.resolve(KrbAsReqBuilder.java:312)
>         at sun.security.krb5.KrbAsReqBuilder.action(KrbAsReqBuilder.java:498)
>         at sun.security.krb5.internal.tools.Kinit.acquire(Kinit.java:248)
>         at sun.security.krb5.internal.tools.Kinit.<init>(Kinit.java:134)
>         at sun.security.krb5.internal.tools.Kinit.main(Kinit.java:96)

Referrals aren't involved here, same realm.
The failing code block is from:
* 
https://github.com/AdoptOpenJDK/openjdk-jdk8u/blob/9a751dc19fae78ce58fb0eb176522070c992fb6f/jdk/src/share/classes/sun/security/krb5/KrbKdcRep.java#L58-L71
* 
https://github.com/AdoptOpenJDK/openjdk-jdk/blob/ff4997014fe5462dca2b313f3f483400ffee5b62/src/java.security.jgss/share/classes/sun/security/krb5/KrbKdcRep.java#L58-L71

>         // sname change in TGS-REP is allowed only if client
>         // sent CANONICALIZE and new sname is a referral of
>         // the form krbtgt/TO-REALM.COM at FROM-REALM.COM.
>         if (!req.reqBody.sname.equals(rep.encKDCRepPart.sname)) {
>             String[] snameStrings = rep.encKDCRepPart.sname.getNameStrings();
>             if (isAsReq || !req.reqBody.kdcOptions.get(KDCOptions.CANONICALIZE) ||
>                     snameStrings == null || snameStrings.length != 2 ||
>                     !snameStrings[0].equals(PrincipalName.TGS_DEFAULT_SRV_NAME) ||
>                     !rep.encKDCRepPart.sname.getRealmString().equals(
>                             req.reqBody.sname.getRealmString())) {
>                 rep.encKDCRepPart.key.destroy();
>                 throw new KrbApErrException(Krb5.KRB_AP_ERR_MODIFIED);
>             }
>         }

So it either fails for
> isAsReq 
or
> !rep.encKDCRepPart.sname.getRealmString().equals(
>>                             req.reqBody.sname.getRealmString())

Here is MIT Kerberos:
> $ kinit OSIPOVMI at ad001.siemens.net
> Passwort für OSIPOVMI at ad001.siemens.net:
> $ klist
> Ticketzwischenspeicher: FILE:/tmp/krb5cc_722
> Standard-Principal: osipovmi at AD001.SIEMENS.NET
> 
> Valid starting       Expires              Service principal
> 20.10.2021 10:02:14  20.10.2021 20:02:14  krbtgt/AD001.SIEMENS.NET at AD001.SIEMENS.NET
>         erneuern bis 21.10.2021 10:02:10

Works as expected. Can someone explain? Shall I create a bug for this?

Michael


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