By SABC Sport
13th December 2023
It means that the England number eight is free to play immediately, making him available for Saturday's European appointment with Connacht.
Vunipola was sent off early in the second half by Italian referee Andrea Piardi for a dangerous strike to the head area of Bulls forward Cameron Hanekom.
The 31-year-old, who appeared by video link before an independent disciplinary panel, accepted that he had committed an act of foul play, but he did not accept it warranted a red card.
Tournament organiser European Professional Club Rugby said: "The committee determined that Vunipola had committed an act of foul play.
"However, it decided that there was insufficient force in the contact to Hanekoms head to warrant a red card, and the red card was therefore overturned.
"Vunipola is free to play immediately, and EPCR has the right to appeal the decision."
Saracens were beaten 27-16 by the Bulls in the first of their four Champions Cup pool games.