Silo focuses mainly on leveraging Oracle to obtain a shell and escalate privileges. It was intended to be completed manually using various tools, however Oracle Database Attack Tool greatly simplifies the process, reducing the difficulty of the machine substantially.

Grandpa is one of the simpler machines on Hack The Box, however it covers the widely-exploited CVE-2017-7269. This vulnerability is trivial to exploit and granted immediate access to thousands of IIS servers around the globe when it became public knowledge.

Arctic is fairly straightforward, however the load times on the web server pose a few challenges for exploitation. Basic troubleshooting is required to get the correct exploit functioning properly.

Granny, while similar to Grandpa, can be exploited using several different methods. The intended method of solving this machine is the widely-known Webdav upload vulnerability.

Bastard is not overly challenging, however it requires some knowledge of PHP in order to modify and use the proof of concept required for initial entry. This machine demonstrates the potential severity of vulnerabilities in content management systems.

Optimum is a beginner-level machine which mainly focuses on enumeration of services with known exploits. Both exploits are easy to obtain and have associated Metasploit modules, making this machine fairly simple to complete.

Devel, while relatively simple, demonstrates the security risks associated with some default program configurations. It is a beginner-level machine which can be completed using publicly available exploits.

Blue, while possibly the most simple machine on Hack The Box, demonstrates the severity of the EternalBlue exploit, which has been used in multiple large-scale ransomware and crypto-mining attacks since it was leaked publicly.