title: PHP GET variable array injection
body: <p>I've recently learned that it's possible to inject arrays into PHP GET variables to perform code execution?</p>
  
  <p><code>.php?a[]=asd&amp;a[]=asdasd&amp;b[]=$a</code></p>
  
  <p>That was the example I was given. I have no idea how it works and was wondering if this is even possible?</p>