Kerberos Detected

Updated (3.1.2)

CVE 2000-0389
CVE 2000-0390
CVE 2000-0391

Impact

If any services which use a vulnerable version of Kerberos are enabled, remote root access may be possible due to a buffer overflow condition. If the Key Distribution Center is affected, the entire Kerberos domain could be compromised.

Background

Kerberos is used to provide strong authentication and encryption between a client and a server. A Kerberos Distribution Center, consisting of an authentication server and a ticket granting server, is involved in the authentication process. Cryptography is used to verify the identity of the user and the server, and to encrypt the session between them.

The Problem


Vulnerabilities in MIT/Cygnus versions

Four buffer overflow conditions have been discovered in Kerberos. The most serious one could allow remote root access if any of the following services are running.

Another buffer overflow condition could allow a local attacker to gain root access by exploiting v4rcp or ksu.

The following implementations of Kerberos are affected by these vulnerabilities:


Vulnerabilities in KTH version

Three vulnerabilities have been discovered in the KTH version of Kerberos, which is included in OpenBSD and FreeBSD operating systems. Two of these vulnerabilities can be used in conjuction with each other to gain root access on an affected system. The first vulnerability allows a remote telnet user to pass environment variables through the telnet session without requiring a local user account. By resetting the krb4_proxy variable, an attacker could cause the Kerberos authentication requests to go to a fake server, thus fooling the system into accepting a false reply. The second vulnerability, a buffer overflow condition in the code which processes authentication replies, could be used with the first vulnerability to gain root access.

The third vulnerability could allow arbitrary files to be overwritten on the system. Ticket files are created in the /tmp directory with predictable file names. A user with an account on the system could guess the file name of a future ticket file, and symbolically link that file name to an arbitrary file on the system. When the ticket file is created, the arbitrary file is overwritten.

Resolution

To fix the problems in the MIT version, upgrade to Kerberos version krb5-1.2, or install the appropriate patches to fix the problem.

Alternatively, the problems in some of the services can be fixed with the following workarounds:

To fix the vulnerability in the KTH version, see the posting to Bugtraq.

Where can I read more about this?

More information is available from CERT Advisory 2000-06 or the Kerberos advisory.