On September 27th, in a security notice Canonical published details about a libxml2 vulnerability for its Ubuntu 12.04 LTS, Ubuntu 11.10, Ubuntu 11.04, Ubuntu 10.04 LTS, and Ubuntu 8.04 LTS operating systems.
According to Canonical, applications using libxml2 could have been made to crash or run programs if users opened a specially crafted file.
Juri Aedla, the user who discovered the vulnerability, if a user or application linked against libxml2 were tricked into opening a specially crafted XML file, an attacker could execute arbitrary code with the privileges of the user.
The security flaws can be fixed if you upgrade your system(s) to the latest libxml2, version. 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.