The Tigers were edged out of the automatic promotion places on Friday night by Leicester after their 1-0 home win over Middlesbrough but it looked like Steve Bruce's team would leapfrog the Foxes after Joe Newell's first-half own goal put them ahead.
However, Peterborough saved themselves from a 10th home league loss 11 minutes from time when McCann scored from the spot.
It meant Posh drew a league game at London Road for the first time since April 21.
Dwight Gayle was unable to add to the 10 goals he has scored for Peterborough since his arrival on loan from Dagenham & Redbridge at the end of November when he headed wide after eight minutes.
Jaanai Gordon-Hutton threatened with a shot from the edge of the area shortly afterwards before Robbie Brady did likewise at the other end midway through the first half.
Liam Rosenior, Nick Proschwitz and Paul McShane all had headers at goal before the half-hour mark - but Posh did not heed the warnings and fell behind in the 31st minute following another cross into their box.
Robert Koren whipped his corner in at the near post and Newell inadvertently diverted the ball past Robert Olejnik.
Gordon-Hutton and on-loan Manchester United youngster Davide Petrucci, making his home debut, went close with efforts from outside the area either side of the half-time whistle.
Stephen Quinn replied for Hull just before the hour and the enthusiastic Gordon-Hutton sent in another shot with 15 minutes remaining.
The hosts equalised after 79 minutes from the penalty spot after Tommy Rowe was brought down by Tigers defender James Chester.
The in-form Gayle wanted to take the spot-kick but McCann took the ball off him and stroked his shot past Stockdale.
Peterborough survived a late scare when substitute Tom Cairney swung in a corner and McShane's diving header had to be parried away by Olejnik.