Maybe I'm getting things mixed up, but I thought Cohen taped conversations with both Trump and Cuomo. I was speaking specifically to taping his client, Trump (or a lawyer taping any client and then having that tape allowed as evidence).
If it's a tape of him speaking with his client and the client hasn't authorized the release, I would think that crosses a serious legal line. But, hey, I'm not an attorney.
*edit to add* Went back to the Fox News story. It looks like there are two parts.
First is Cohen's conversation with Chris Cuomo from CNN. Cohen specified he wasn't recording the conversation when he really was. Cuomo wasn't his client so no client/attorney privilege on releasing the tape, or so I would presume. That still leaves a big professional ethics question with regard to doing something when you specifically stated you weren't.
Second is Cohen's release, via his attorney, of a conversation with Trump about purchasing story rights to Karen McDougal's story of the purported 2006 affair with Trump. This is a big attorney/client question. If Trump didn't authorize the release then Cohen is in heap big hot water. Possibly his attorney, too, for being complicit in the release.
In general it sounds like this guy is a complete slimeball with nothing in the way of personal ethics and very little in the way of professional ethics.
Brad