Canonical announced on September 6th, in a security notice, that a new Linux kernel update for its Ubuntu 11.04 (Natty Narwhal) operating system is available for all users.
There's a single kernel vulnerability (CVE-2012-3400), discovered by various developers, related to some errors found in Linux kernel's UDF file system (used to mount DVDs and CD-ROMs), which could allow an unprivileged local user to crash the system.
As usual, you can click on it to see how it affects your system, or go here for in-depth descriptions, as it affects other Linux operating systems as well.
Ubuntu 11.04 users can fix the security flaw if they upgrade to the linux-image-2.6.38-15 (2.6.38-15.66) package(s). To apply the update, run the Update Manager application or take a look at some detailed instructions: https://wiki.ubuntu.com/Security/Upgrades.
Don't forget to reboot your computer after the upgrade!