apt-cache policy wpasupplicant                                                     # this prints the wpasupplicant versions available on your system. 

# Select one of following versions (stretch or jessie). Selection is based on your config inside /etc/apt/sources.list
# Note that the version numbers could be different on your system! Check the apt-cache policy wpasupplicant output for certainty! 
sudo apt-get install sudo apt-get install wpasupplicant=2:2.4-1+deb9u7 -t stretch  # package of choice is printed by the previous command.
sudo apt-get install wpasupplicant=2.3.1+deb8u10 -t jessie                         # package of choice is printed by the previous command.