How to convert date format in file

Input file: Contains 3 columns with the 3rd column is date in DD-MMM-YYYY format

sample data:

1232,abdc, 02-Jan-2014
4534,kdafh, 20-Feb-2014
364,asjhdk, 11-Jul-2012

required output:

1232,abdc, 2014-01-02
4534,kdafh, 2014-02-20
364,asjhdk, 2012-07-11

using function date: date -d 20-DEC-2014 +%Y-%m-%d

used it awk command gives error

Is there any other way?