If it was only the impact that shunted you into the car in front (ie you had stopped completely, handbrake on, etc), then the fault is entirely down to the person who struck you in the rear.
Any insurer will ask all parties involved how many impacts they felt, etc, and the engineering evidence will tell the true story in disputed cases.
There cannot be liability assigned to you for being too close to the vehicle in front if you were stationary at the time - who realistically leaves a car length between them when sat in traffic