Some of the most popular Java projects in the JVM ecosystem are vulnerable to a MITM of their dependencies. This is something that build tools can help prevent.
Starting in the next release of Maven, Maven should begin warning users about the use of HTTP to download/upload artifacts to/from artifact servers.
I believe that Maven/Gradle/SBT should require users to opt-out of the security offered by using HTTPS to download/upload artifacts.
Here's a list of projects that were found to be vulnerable to this:
The full description of this industry-wide vulnerability can be found here: