Shellshock Tutorial : Shellshock Attack to Gain Root Access into a Computer in Same Lan?

Hello . i wanna ask for a help about shellshock . i have 2 virtual MACHINES . one is ubuntu and the other one is metasploitable 2 system . i want to get root access with shellshock into metasploitable2 from ubuntu .(metasploitable 2 system has a login password and we dont know it). what kind of methods can we use ?

Thanks...