What is this cable called?
As @Venny has said, it looks to be a custom connector. It looks like a press fit, non-latching, 0.1" header for external use. If you measure it out to confirm, you could make your own using 6x2 male and female Headers, or a 6x2 idc cable with a set of 6x2 male 0.1" header placed in one end as an adapter.

It may not fit in the male receptor, so you may think about cutting and splicing a longer cable in the middle.