The upstream library for the Ruby uglifier gem, UglifyJS, is affected by a vulnerability that allows a specially crafted Javascript file to have altered functionality after minification.

This bug, found in UglifyJS versions 2.4.23 and earlier, was demonstrated to allow potentially malicious code to be hidden within secure code, and activated by the minification process.

For more information, consult: https://zyan.scripts.mit.edu/blog/backdooring-js/