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Category:   Application (Security)  >   Kerberos Vendors:   Royal Institute of Technology
Heimdal Kerberos Cross-Realm Validation Flaw May Permit User Impersonation
SecurityTracker Alert ID:  1009646
SecurityTracker URL:  http://securitytracker.com/id/1009646
CVE Reference:   CVE-2004-0371   (Links to External Site)
Updated:  Apr 30 2004
Original Entry Date:  Apr 2 2004
Impact:   Host/resource access via network, Modification of user information
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): prior to 0.6.1 and 0.5.3
Description:   A cross-realm vulnerability was reported in Heimdal Kerberos. A remote user can impersonate another user.

The vendor reported that a user with with control of a Kerberos realm can impersonate any target user in the cross-realm trust path. The software does not properly perform consistency checks on cross-realm requests.

The advisory is available at:

http://www.pdc.kth.se/heimdal/advisory/2004-04-01/

Impact:   A user with with control of a Kerberos realm can impersonate any target user in the cross-realm trust path.
Solution:   The vendor has released fixed versions (0.6.1 and 0.5.3), available at:

ftp://ftp.pdc.kth.se/pub/heimdal/src/

Vendor URL:  www.pdc.kth.se/heimdal/ (Links to External Site)
Cause:   Authentication error
Underlying OS:  Linux (Any), UNIX (Any)

Message History:   This archive entry has one or more follow-up message(s) listed below.
Apr 7 2004 (Debian Issues Fix) Heimdal Kerberos Cross-Realm Validation Flaw May Permit User Impersonation
Debian has released a fix.
Apr 10 2004 (Gentoo Issues Fix) Heimdal Kerberos Cross-Realm Validation Flaw May Permit User Impersonation
Gentoo has released a fix.
May 6 2004 (FreeBSD Issues Fix) Heimdal Kerberos Cross-Realm Validation Flaw May Permit User Impersonation
FreeBSD has released a fix.
May 31 2004 (OpenBSD Issues Fix) Heimdal Kerberos Cross-Realm Validation Flaw May Permit User Impersonation
OpenBSD has issued a fix.



 Source Message Contents

Subject:  http://www.pdc.kth.se/heimdal/advisory/2004-04-01/


http://www.pdc.kth.se/heimdal/advisory/2004-04-01/

2004-04-01: Cross-realm trust vulnerability in Heimdal

All releases prior to 0.6.1 and 0.5.3 have a cross-realm vulnerability allowing someone 
with control over a realm to impersonate anyone in the cross-realm trust path.

0.6.1 and 0.5.3 performs proper consistency checks on cross-realm requests, as well as 
allowing for better control over transit checks.

If you are running a vulnerable KDC version and have established cross-realm trust with 
anyone, we recommend that you disable this trust and then upgrade to 0.6.1.

Too see if you have any cross-realm trust enabled you can list all krbtgt principals in 
the database:

kadmin> get -t krbtgt/*
   krbtgt/<MY.REALM>@<MY.REALM>
   krbtgt/<MY.REALM>@<OTHER.REALM>
   krbtgt/<OTHER.REALM>@<MY.REALM>

If you have any <OTHER.REALM> variants, you can temporarily disable them with:

kadmin> mod krbtgt/<MY.REALM>@<OTHER.REALM>
Max ticket life [unlimited]:
Max renewable life [unlimited]:
Principal expiration time [never]:
Password expiration time [never]:
Attributes []:+disallow-all-tix

You have to repeat this for all such principals as there is no easy way to automate this. 
If you have a huge number to update, you will probably have to dump the database, edit the 
dump, and reload. After upgrading the KDC you can reenable them with:

kadmin> mod krbtgt/<MY.REALM>@<OTHER.REALM>
Max ticket life [unlimited]:
Max renewable life [unlimited]:
Principal expiration time [never]:
Password expiration time [never]:
Attributes [disallow-all-tix]:-disallow-all-tix

See also CAN-2004-0371.


 
 


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