In Oracle after upgrade, we are getting error for our user login.
ORA-01017: invalid username/password;

Cause:
Oracle introduced the password versions in dba_users which will defined the password is supported 10g, 11g and 12c but when we upgrade to 12.2 version then sqlnet.ora file use default value for the SQLNET.ALLOWED_LOGON_VERSION_SERVER parameter is “12”. Which cause the error for the old using version.

Check the version of password using by user.

SELECT USERNAME,PASSWORD_VERSIONS FROM DBA_USERS;

Solution:

1. In 12c or upper version, its also recommended to use case sensitivity for that parameter value is true. alter this database parameter SEC_CASE_SENSITIVE_LOGON = TRUE for setting case sensitivity.
2. Edit the SQLNET.ora file and lower the default value of parameter SQLNET.ALLOWED_LOGON_VERSION_SERVER to a lower version (12.2)

--Set 8 for Password Versions 10G, 11G and 12c
SQLNET.ALLOWED_LOGON_VERSION_SERVER=8 or 11

---Set 12 for the 11G and 12c password Versions
SQLNET.ALLOWED_LOGON_VERSION_SERVER=12

---Set the 12c for the only 12c Password Versions
SQLNET.ALLOWED_LOGON_VERSION_SERVER=12a

3. After setting the parameter in SQLNET.ORA, then you can reset your username and password for generating all version.