Source : WordNet®

magic bullet
     n : a remedy (drug or therapy or preventive) that cures or
         prevents a disease; "there is no magic bullet against
         cancer"

Source : Free On-Line Dictionary of Computing

magic bullet
     
         (Or "silver bullet" from vampire legends) A term
        widely used in software engineering for a supposed quick,
        simple cure for some problem.  E.g. "There's no silver bullet
        for this problem".
     
        (1999-01-13)