Who is violating the law by discussing Mueller's grand jury actions with the media?

NY Post Editorial:

Another day, another potentially illegal leak from special counsel Robert Mueller’s grand jury investigating Russian election meddling.

NBC News reported Monday that Mueller has “gathered enough evidence” to indict former National Security Adviser Michael Flynn and his son.

This followed the earlier leak to CNN — 72 hours in advance — that the grand jury had voted the first indictments in the investigation, later identified as former campaign chairman Paul Manafort and his business associate, Rick Gates.

And that raises the suspicion that the special counsel may be playing politics with his prosecutions.
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Rep. Trey Gowdy (R-SC), chairman of the House Committee on Oversight and Government Reform, says he specifically warned Mueller about “the importance of cutting out the leaks.”

Indeed, he added on Fox News Sunday, “it’s kind of ironic that the people charged with investigating the law and the violations of the law would violate the law.”
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This looks like a prosecutor playing politics.  Can't Mueller even write a memo to the staff telling them to cut it out?