CVE-2019-9949: Critical severity western digital my cloud firmware vulnerability

Western Digital My Cloud Cloud, Mirror Gen2, EX2 Ultra, EX2100, EX4100, DL2100, DL4100, PR2100 and PR4100 before firmware 2.31.183 are affected by a code execution (as root, starting from a low-privilege user session) vulnerability. The cgi-bin/webfilemgr.cgi file allows arbitrary file write by abusing symlinks. Specifically, this occurs by uploading a tar archive that contains a symbolic link, then uploading another archive that writes a file to the link using the "cgiuntar" command. Other commands might also be susceptible. Code can be executed because the "name" parameter passed to the cgiunzip command is not sanitized.