ORA-1017 Invalid Username or Password on 19c while credentials are correct

 Problem:

After upgrading a DB to 19c version, some legacy applications cannot connect to the DB, throwing the error "ORA-1017 Invalid Username or Password" although the login details are correct and work fine from SQLPlus and other non-legacy applications.

 
Analysis:

- sqlnet.ora file already has the following parameters which allows legacy Oracle clients to connect:

- Enabling or disabling sec_case_sensitive_logon parameter doesn't solve the issue:

when checking the password version for the user the legacy application trying to connect with, I can see it's 11G 12c:

SQL> select username,password_versions from dba_users where username='LEGACY_APP';
 

 
Solution:

Resetting the user's password --even to the same password from SQLPlus will set it to 10G version and will allow legacy applications to connect suing that user:

SQL> alter user LEGACY_APP identified by Legacy_123;

Now, the password version supports 10G:

SQL> select username,password_versions from dba_users where username='LEGACY_APP';
 

Reference:

https://docs.oracle.com/en/database/oracle/oracle-database/18/upgrd/case-insensitive-passwords-ora-1017-invalid-username-password.html#GUID-FDA9C77A-12F4-4410-9448-9BCC13960C27