Kerberos is a network authentication system which allows clients and servers to authenticate to each other through use of symmetric encryption and a trusted third party, the KDC.
A flaw was found in the username handling of the MIT krb5 telnet daemon (telnetd). A remote attacker who can access the telnet port of a target machine could log in as root without requiring a password. (CVE-2007-0956)
Note that the krb5 telnet daemon is not enabled by default in any version of Red Hat Enterprise Linux. In addition, the default firewall rules block remote access to the telnet port. This flaw does not affect the telnet daemon distributed in the telnet-server package.
For users who have enabled the krb5 telnet daemon and have it accessible remotely, this update should be applied immediately.
Whilst we are not aware at this time that the flaw is being actively exploited, we have confirmed that the flaw is very easily exploitable.
This update also fixes two additional security issues:
Buffer overflows were found which affect the Kerberos KDC and the kadmin server daemon. A remote attacker who can access the KDC could exploit this bug to run arbitrary code with the privileges of the KDC or kadmin server processes. (CVE-2007-0957)
A double-free flaw was found in the GSSAPI library used by the kadmin server daemon. Red Hat Enterprise Linux 4 and 5 contain checks within glibc that detect double-free flaws. Therefore, on Red Hat Enterprise Linux 4 and 5 successful exploitation of this issue can only lead to a denial of service. Applications which use this library in earlier releases of Red Hat Enterprise Linux may also be affected. (CVE-2007-1216)
All users are advised to update to these erratum packages which contain a backported fix to correct these issues.
Red Hat would like to thank MIT and iDefense for reporting these vulnerabilities.