In a security notice, Canonical has published details about a Remote Login Service vulnerability for its Ubuntu 12.10 (Quantal Quetzal) operating system.
According to Canonical, the Remote Login Service could have been made to expose sensitive information.
It was discovered that Remote Login Service incorrectly purged account information when switching users. A local attacker could have used this issue to possibly obtain sensitive information.
For a more detailed description of the security problems, you can visit Canonical's security notification.
Users can fix the security flaw by simply upgrading the operating system to the latest remote-login-service package.
A normal system update, executed with the Update Manager, will implement all the necessary changes, but you will also need to reboot the computer.
To update your system, please follow the instructions on this page: https://wiki.ubuntu.com/Security/Upgrades.