Redcross is a machine on hackthebox.eu, featuring sql injection, cookie reuse and a nice binary exploitation challenge, which I enjoyed a lot.
LaCasaDePapel is a rather easy machine on hackthebox.eu, featuring the use of php reflection, creating and signing of client certificates and the abuse of a cronjob. Unfortunately the box was very unstable and slow for me and therefore pretty unenjoyable.
Curling is one of the easier boxes on hackthebox.eu, featuring getting a shell on joomla via template editing, getting a password from an obfuscated file and exploiting an insecure curl script.
Frolic is a medium difficulty machine on hackthebox.eu, featuring a lot of CTF-ish language conversions, the usage of a public exploit for "playsms" and (simple) custom binary exploit.
Carrier is a nice, medium difficulty machine on hackthebox.eu featuring information retrieval via snmp, command injection and bgp hijacking. The bgp hijacking part was a nice learning experience as this is a technique you probably don't see every day.
This post is a walkthrough of Zipper, an interesting machine on hackthebox.eu featuring the zabbix network monitoring application. It involves the application of known zabbix exploits, manipulation of database entries and light custom exploitation of a privileged binary.