sudo, when linked with MIT Kerberos 5 (krb5), does not properly check whether a user can currently authenticate to Kerberos, which allows local users to gain privileges, in a manner unintended by the sudo security model, via certain KRB5_ environment variable settings.  NOTE: another researcher disputes this vulnerability, stating that the attacker must be "a user, who can already log into your system, and can already use sudo."