Vacuum is a space with no matter or with such little pressure that whatever particles throughout the space have had no effect on any activities taking place.
The temperature must've been zero according to the definition of vacuum. However, zero temperature is not possible according to the third rule of thermodynamics.
As a result, it may be stated that there is no perfect vacuum, and even if there were, the temperature would've been zero.
Therefore, the temperature in a vacuum must be zero.