Boss Gary Waddock told the club website: "Bully has played at a consistently high level this season but I didn't expect anything else.
"When we brought him in six months ago, we knew we were signing one of the best keepers in the lower leagues."
Bull, who played over 200 times for Aldershot between 2002 and 2009, has kept 11 clean sheets this season.
Steve Hayes [Wycombe owner] has put his faith in me once again and backed me
Wycombe boss Gary Waddock
Most recently he kept promotion rivals Rotherham at bay to help secure a 1-0 win for the Chairboys.
"I'm delighted. I've never enjoyed my football more than I am now," he said.
"I've got a great relationship with the manager, players and the fans. It was a no-brainer."
Waddock added: "Steve Hayes [Wycombe owner] has put his faith in me once again and backed me in being able to keep a very important player at the club.
"I think it's important for us to have a close working relationship and that has helped the progression of the club."
Source: BBC Sport