The remote Debian host is missing a security-related update.
Vadim Melihow discovered that in proftpd-dfsg, an FTP server, the mod_copy module allowed unauthenticated users to copy files around on the server, and possibly to execute arbitrary code.
Upgrade the proftpd-dfsg packages. For the oldstable distribution (wheezy), this problem has been fixed in version 1.3.4a-5+deb7u3. For the stable distribution (jessie), this problem has been fixed in version 1.3.5-1.1+deb8u1.