Does this break via the UI, REST API, or the command line?
Could it be the shell eating the characters?
I changed my admin user's password in a test instance like so:
prompt$ splunk login
Splunk username: admin
Password: <-entered old password here
prompt$ splunk edit user admin -password 'star*'
User admin edited.
prompt$ splunk login
Splunk username: admin
Password: <-entered star* here
prompt$ splunk search 'index=_internal |head 10 |stats count'
count
-----
10
prompt$ splunk search 'index=_internal |head 10 |stats count' -auth 'admin:star*'
count
-----
10
The UI worked fine too.
Thanks for your reply Martin
Log in to your Splunk instance, click your user name in the top bar, select Edit Account, type in your new password twice, and hit save.
That's for Splunk's local authentication, if you're using external authentication such as LDAP you'll need to change your password there.