Todas as conexões do mesmo host serão feitas através da interface lo
(loopback), que não é restrita por padrão e permitida colocando a linha no topo das regras:
-A INPUT -i lo -j ACCEPT
A atualização automática do Wordpress geralmente funciona sem acesso ao FTP, se não - deve haver um limite de segurança muito rígido no servidor web / php. Normalmente o wordpress está verificando o espaço em disco e as permissões com algumas funções feias (AFAI lembra, havia algo relacionado a verificações de inodes (WEIRD)).
For Automatic Update to work, at least two criteria must be satisfied:
(a) file ownership: all of your WordPress files must be owned by the user under which your web server executes. In other words, the owner of your WordPress files must match the user under which your web server executes. The web server user (named "apache", "web", "www", "nobody", or some such) is not necessarily the owner of your WordPress files. Typically, WordPress files are owned by the ftp user which uploaded the original files. If there is no match between the owner of your WordPress files and the user under which your web server executes, you will receive a dialog box asking for "connection information", and you will find that no matter what you enter in that dialog box, you won't be able to update automatically.
(b) file permissions: all of your WordPress files must be either owner writable by, or group writable by, the user under which your Apache server executes.
On shared hosts, WordPress files should specifically NOT be owned by the web server. If more then one user owns different files in the install (because of edits made by deleting and re-uploading of files via different accounts, for example), the file permissions need to be group writable (for example, 775 and 664 rather then the default 755 and 644). File permissions (in general) should be adjusted as appropriate for the server environment (the shared host RackSpace CloudSites for example recommends 700 and 600 for a single ftp user, or 770 and 660 for multiple ftp users). See the file permission section for more (some files and folders require stricter permissions).
(c) link
Verifique se há permissões, etc.
Se você ainda quiser fazer isso com o FTP, certifique-se de ouvir o endereço local também netstat -anp|grep 21
.
SFTP? Mesmo? Você não quer fazer isso. Acredite em mim.