Ubuntu Security Notice 638-1 – Aaron Grattafiori discovered that the Gnome Help Viewer did not handle format strings correctly when displaying certain error messages. If a user were tricked into opening a specially crafted URI, a remote attacker could execute arbitrary code with user privileges.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/69459/USN-638-1.txt
Source: https://packetstormsecurity.com/files/69459/Ubuntu-Security-Notice-638-1.html