The vulnerability resides in ProFTPds mod_copy module that supplied with the default installation. The vulnerability can be tracked as CVE-2019-12815 and affects all the versions up to 1.3.5b. According to Shodan results, more than 1 Million Servers running vulnerable versions of the ProFTPD. In future attackers may use exploits to compromise the vulnerable servers and infect them with malware. The most used operating system are Linux ones and the most used system is Linux ones.”]
Source: https://gbhackers.com/proftpd-file-copy-vulnerability/