Cybercriminals are exploiting a ThinkPHP vulnerability — one that was disclosed and patched in December 2018 — for botnet propagation by a new Mirai variant we’ve called Yowai and Gafgyt variant Hakai. Cybercriminals use websites created using the PHP framework to breach web servers via dictionary attacks on default credentials and gain control of these routers for distributed denial of service attacks (DDoS). Our telemetry showed that these two particular malware types caused a sudden increase in attacks and infection attempts from January 11 to 17.

https://blog.trendmicro.com/trendlabs-security-intelligence/thinkphp-vulnerability-abused-by-botnets-hakai-and-yowai/