brakes soft after car sat for a few months?

[93 saturn sl2]

I fired up my Explorer the other day and drove it around after sitting outside since April. When I parked it the brakes worked like normal. Now when I press the pedal it feels soft and goes to the floor easily. I can still stop but its not safe. Any explanation as to what happened over the summer?

 

[1BADAIR]

no leaks? abs valve leaking internally, rotors rusty?

 

[93 saturn sl2]

The rotors were rusty like any other car that has sat outside in the elements. There are no leaks that I could see.

I plan on doing a flush so ill see if that fixes the problem. I was just curious as to how that could happen.

 

[Beigg]

leaking master/booster