"pretty easily" all 5 kage at the same time?
OP: This is really hard to decide. Kabuto winning isn't very likely, but it's possible
Kabuto has full intel and is inside Ryuchi Cave. They'll be completely vulnerable to Muki Tensei and White Rage under these conditions and will lose several members right off the bat. The rest will have to contend with Kimimaro's Bone Forest, Kabuto's Sage sensing and the LoS type area their in allow him to maneuver freely and dodge easier, Tayuya's Sound Genjutsu is a big threat in this enclosed area, the Kage have 0 intel on Kabuto so they have no clue about his Oral Rebirth or Manda II wildcards.
Not to mention Kabuto is a genius and will be picking them off the appropriate order e.g. taking out Tsunade early so she can't transfer chakra/heal the others, used the Muki Tensei and cave location to play against Onoki's flight, Ay will engage in taijutsu immediately and will either be dodged or face the Hozuki Hydrification technique and be ripe for the killing, etc.
But then again I'm not exactly an expert on DSM Kabuto. But I feel, with these conditions, he'd win moderate difficulty.