14 DAY TRIAL // Canonical published details in a security notice about an NSS vulnerability in its Ubuntu 13.10, Ubuntu 13.04, Ubuntu 12.10, Ubuntu 12.04 LTS, and Ubuntu 10.04 LTS.
According to the company, several security issues have been fixed in NSS.
A number of security problems have been discovered in NSS. If a user was tricked into connecting to a malicious server, an attacker could have possibly exploited this to cause a denial of service via application crash, potentially execute arbitrary code, or lead to information disclosure.
For a more detailed description of the problems, you can see Canonical's security notification.
The security flaws can be fixed if you upgrade your system(s) to the latest libnss3 package specific to each distribution. To apply the update, run the Update Manager application.
In general, a standard system update will make all the necessary changes, but this time a system restart will be needed to implement them.