Ireland will face group leaders Germany in Dublin on Tuesday and their captain Cullen is aiming for a victory that would see them surpass the Germans.
"We've got three games left in the campaign and I think this home match against Germany is one we have to win," Cullen, currently on loan at Charlton Athletic,told West Ham official website.
"All of the games at the business end are must-wins in my view and I believe we're capable of beating Germany.
"That draw in Kosovo might turn out to be a good point, as other nations have struggled to get anything off them. It wasn't our best display and we're capable of playing better."