Problem

How to change user account password over FTP or FTPS (UNIX)?

Resolution

After logging in as the user, the change password syntax would be:
SITE CHPWD <account_name> <old_password> <new_password>

However, there is a limitation, all the parameters must be base64 encoded.

With this in mind, here is an example:
- <account_name> = test
- <old_password> = SECRET
- <new_password> = SECRET123

1. Encode the parameters
# echo -n test|base64
dGVzdA==
# echo -n SECRET|base64
U0VDUkVU
# echo -n SECRET123|base64
U0VDUkVUMTIz

2. Login and change password
ftp localhost
Connected to localhost.
220 ST 5.x FTP server (SecureTransport 5.x) ready.
Name (localhost:root): test
331 Password required for test.
Password:
230 Virtual user test logged in.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> quote
(command line to send) SITE CHPWD dGVzdA== U0VDUkVU U0VDUkVUMTIz
200 CHPWD command successful.
ftp> quit
221 Goodbye.

*NOTE* The examples use native UNIX utilities. Different operating systems or utilities may behave differently.