I've been setting up some Ubuntu Jaunty systems for relatives as an excuse to get rid of a lot of old hardware including some SCSI scanners. I encountered an HP scanner that was supported by sane but not recognized by Ubuntu. The device ended up with the wrong permissions preventing anyone except root from scanning.

Hotplugging (which is the word used to describe the process of inserting devices into a running system) is achieved in a Linux distribution by a combination of three components: Udev, HAL, and Dbus.

Brad Spengler, the developer behind the Grsecurity project, has published an exploit for a vulnerability in the Tun interface in Linux kernel 2.6.30 and 2.6.18, used in Red Hat Enterprise Linux 5 (RHEL5), which can be exploited by attackers to obtain root privileges. Of particular interest is the fact that the exploit is even able to circumvent security extensions such as SELinux.

A Linux kernel bug in network socket initialization could allow an attacker to acquire root privileges to inflict damages. The security hole applies to all kernels of the 2.4 and 2.5 series and has been around possibly since 2001.

A vulnerability has been reported in the Linux kernel's memory management allows applications to execute code at root privilege level. The flaw appears to have been introduced into the kernel with version 2.6

Flawed sudo code allows users with limited privileges to obtain root privileges

As you may have read in LWN (subscription required, and strongly recommended anyway), there’s been some argument on the linux-hotplug mailing list, the historically named home of udev development, about device naming.

Devtmpfs, aka 'devfs 2.0' to its detractors, should allow the Linux kernel to start faster and run without udev. Support has been added for ACPI 4.0 and there are two new make targets which generate kernel configurations attuned to the running system. Changes to the power management subsystem increase data throughput and allow better use of runtime power saving features on modern I/O devices.

By default, the root account password is locked in Ubuntu - Canonical neither supports nor advocates enabling the root account. This means that you cannot login as root directly or use the su command to become the root user. However, since the root account physically exists it is still possible to run programs with root-level privileges.