On October 1st, in a security notice Canonical published details about a Software Properties vulnerability for its Ubuntu 12.04 LTS, Ubuntu 11.10, Ubuntu 11.04, and Ubuntu 10.04 LTS operating systems.
According to Canonical
, Software Properties could be tricked into installing arbitrary PPA GPG keys. The apt-add-repository tool incorrectly validated PPA GPG keys when importing from a keyserver. If a remote attacker were able to perform a man-in-the-middle attack, this flaw could be exploited to install altered package repository GPG keys.
The security flaw can be fixed if you upgrade your system(s) to the latest python-software-properties. To apply the update, run the Update Manager application.
In general, a standard system update will make all the necessary changes. A system restart won't be necessary to implement the changes.
If you don't know how to update your system, you can check the official Ubuntu wiki