[原文]passwd before 1:4.0.13 on Ubuntu 6.06 LTS leaves the root password blank instead of locking it when the administrator selects the "Go Back" option after the final "Installation complete" message and uses the main menu, which causes the password to be zeroed out in the installer's memory.
Ubuntu Linux Alternate/Server CD Installer Empty root Password
Local Access Required
Loss of Integrity
Canonical Ltd. Ubuntu contains a flaw that may allow a malicious user to gain access to unauthorized privileges. The issue is triggered when the "Go Back" option is selected after "Installation Complete" message during the installation. This sets the root password to a null string which can be exploited by an attacker to gain unauthorized access to the system.
Upgrade to version 6.06 LTS or higher, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.