Black Cube is no more Israeli intelligence than Blackwater is the USA Marines.
Black Cube is a dirtbag organization of privateers that do dirty tricks for whomever hires them. They hire out of every organization, from the FBI to the FSB to the Mossad. It’s mainly just lawyers and accountants.
Well, the splash page states:
“A select group of veterans from the Israeli elite intelligence units that specialises in tailored solutions to complex business and litigation challenges”
So I’m guessing it’s Israeli intelligence.