Versions from 1.98 to 2.02 (December, 2015) are affected. The vulnerability can be exploited under certain circumstances, allowing local attackers to bypass any kind of authentication (plain or hashed passwords) And so, the attacker may take control of the computer. To quickly check if your system is vulnerable, when the Grub ask you the username, press the Backspace 28 times. If your machine reboots or you get a rescue shell then your Grub is affected. This results in an incalculable number of affected devices.”]
Source: http://hmarco.org/bugs/CVE-2015-8370-Grub2-authentication-bypass.html