After the match - which Palace won 3-0 - Cardiff owner Vincent Tan accused Eagles sporting director Iain Moody of using his contacts at his former club to obtain Ole Gunnar Solskjaer's starting XI in the days before the game.
Cardiff sacked a club employee and reported the incident to the Premier League, who have now found Palace guilty of breaching rule B.16 and fined them an undisclosed amount, which rule W.8 states cannot exceed £25,000.
Premier League rule B.16 states that "In all matters and transactions relating to the League each Club shall behave towards each other Club and the League with the utmost good faith".
Palace's punishment is unlikely to satisfy Tan or Cardiff, who suffered relegation from the Premier League while their opponents eventually finished 11th, 12 points clear of the drop zone.
Former Cardiff boss Malky Mackay is currently among the favourites to join Moody at Selhurst Park as manager, following the surprise departure of Tony Pulis just a day before the start of the new Premier League season.