Update the WordPress SP Project & Document Manager plugin to the latest available version (at least 4.22).
Viktor Markopoulos (vict0ni) discovered and reported this Remote Code Execution (RCE) vulnerability in WordPress SP Project & Document Manager Plugin. This could allow a malicious actor to execute commands on the target website. This can be used to gain backdoor access to then take full control of the website. This vulnerability has been fixed in version 4.22.