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Vulnerability Note VU#684563MIT Kerberos V5 allows inter-realm user impersonation by malicious realm controllers with shared keysOverviewMIT Kerberos V5 contains a flaw that allows the controller of one Kerberos realm to impersonate users in a second realm.I. DescriptionMIT Kerberos V5 releases prior to 1.2.3 contain a vulnerability that allows users from one realm to impersonate users from other non-local realms that use the same (shared) keys. This vulnerability is the result of a flaw in the chk_trans.c file of the libkrb5 library and affects both the Key Distribution Center (KDC) and other Kerberos application servers.II. ImpactThis vulnerability may allow users to gain unauthorized access to other realms, with various impacts possible depending on the Kerberos access control list (ACL) for each realm.III. SolutionUpdate your Kerberos installationThis vulnerability was addressed in MIT Kerberos V5 1.2.3. MIT krb5 Security Advisory 2003-001 provides additional information from MIT and is available at: For information regarding other vendors who may be affected, please see the vendor section of this document. Follow the suggestions in MIT krb5 Security Advisory 2003-001 MIT krb5 Security Advisory 2003-001 provides the following recommendations for sites that are unable to apply a patch immediately:
Delete or change inter-realm keys so inter-realm authentication is disabled. Remove all non-local principals from all critical ACLs in services using old MIT Kerberos code to validate the realm transit path Systems Affected
References
The CERT/CC thanks Joseph Sokol-Margolis and Gerald Britton for discovering this vulnerability and Ken Raeburn of MIT for bringing it to our attention. This document was written by Shawn Van Ittersum and Jeffrey P. Lanza.
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