5/29/01
The FTP daemon included in MIT Kerberos version 5 contains
a buffer overflow which could allow a remote attacker to
execute arbitrary commands with root privileges. In order
to exploit this vulnerability, the attacker would either
need access to an account on the system, or anonymous
FTP would have to be enabled.
krb5-1.2.2 and earlier are affected by this vulnerability.
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.
The following implementations of Kerberos are affected by these vulnerabilities:
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.
To fix the other 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, FreeBSD users should apply the patch referenced in FreeBSD Security Advisory 01:25. OpenBSD users and all other users should refer to the fixes posted to Bugtraq.
More information on the other problems in MIT Kerberos is available from CERT Advisory 2000-06 or the Kerberos advisory.
More information on the vulnerabilities in the KTH version is available from FreeBSD Security Advisory 01:25 or Bugtraq.