A critical flaw was announced today that affects the MIT Kerberos telnet daemon, distributed with all versions of Red Hat Enterprise Linux. With this flaw, an attacker who can access the telnet port of a target machine could log in remotely as root without requiring a password.

The Kerberos 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 is similar to the Solaris telnet daemon flaw reported earlier in the year, but the exact flaw and exploit mechanism are technically slightly different.

While we are not aware of this flaw being actively exploited at this time, we have confirmed that this would not be difficult. We therefore urge all users who have enabled the Kerberos telnet daemon to apply the update as soon as possible, and to disable the daemon in the meantime.

Updated packages to correct this issue, along with more details and advice, are available here, as well as via the Red Hat Network.

Red Hat would like to thank MIT for reporting this flaw. This issue was assigned CVE itentifier CVE-2007-0956 and was reported to the Red Hat security response team on February 21, 2007 with an embargo date of April 3, 2007.