magic bullet 
noun informal
A medicine or other remedy with advanced or highly specific properties: there’s no magic bullet, and we should just try to eat as varied and well-balanced a diet as possible...
- He focused on prevention, lifestyle, and dietary medicine - not magic bullets.
- In the absence of a vaccine and a magic bullet against HIV and the disease it engenders, public health authorities had to develop a comprehensive prevention strategy.
- Even when things are going well, it's natural to become frustrated and wish for a magic bullet to cure your cancer.
Synonyms
solution, answer, resolution, way out;
remedy, antidote, cure, nostrum, panacea
informal quick fix