Mueller scores big win as court rejects challenge to his appointment (Politico). "In a unanimous ruling, a three-judge panel of the D.C. Circuit Court of Appeals turned aside arguments that Mueller wields so much power as a special prosecutor that he should have been nominated by the president and confirmed by the Senate."

What may be more important, at least to Roger Stone, is that the court further determined that Andrew Miller is in contempt of court for not appearing before the grand jury. In Re Grand Jury Investigetion
Because the Special Counsel is an inferior officer, and the
Deputy Attorney General became the head of the Department
by virtue of becoming the Acting Attorney General as a result
of a vacancy created by the disability of the Attorney General
through recusal on the matter, we hold that Miller’s challenge
to the appointment of the Special Counsel fails. Accordingly,
we affirm the order finding Miller in civil contempt.

(Interestingly, there is an implication in the ruling that Whitaker may not have been properly appointed acting AG.)