Two vulnerabilities, one related to Linux kernel's KVM (Kernel Virtual Machine) and a flaw in the Linux kernel causing a reference leak, affecting the Ubuntu 10.04 LTS (Lucid Lynx) operating system, were fixed in the Oneiric Linux kernel backport.
You can click on each one to see how it affects your system, or go here for in-depth descriptions, as it affects other Linux operating systems as well.
The security flaws can be fixed if you upgrade your system(s) to linux-image-3.0.0-26. To apply the update, run the Update Manager application or follow these instructions: https://wiki.ubuntu.com/Security/Upgrades.
Don't forget to reboot your computer after the upgrade!
ATTENTION: Due to an unavoidable ABI change, the kernel packages have a new version number, which will force you to reinstall and recompile all third-party kernel modules you might have installed. Moreover, if you use the linux-restricted-modules package, you have to update it as well to get modules that work with the new Linux kernel version.