It's a strange Common Body of Knowledge if it's not published or available to the members.  It really is security through obscurity!

I would have thought that since the CBK construct is based on work that isn't necessarily proprietary that publishing the CBKs as an outline would not cause harm to ISC2.  Not publishing them when existing members took their CISSP under a previous set of CBKs rather obviously make submitting CPEs a bit of a hit and miss affair.