In 12.1, the default value for the SQLNET.ALLOWED_LOGON_VERSION parameter has been updated to 11. This means that database clients using pre-11g JDBC thin drivers cannot authenticate to 12.1 database servers unless theSQLNET.ALLOWED_LOGON_VERSION parameter is set to the old default of 8.
Very old question but providing some additional information which may help someone else. I also encountered same error and I was using ojdbc14.jar with 184.108.40.206 Oracle Database. On Oracle official web page this information is listed that which version supports which database drivers. Here is the link and it appears that with Oracle 12c and Java 7 or 8 the correct version is ojdbc7.jar.
If you are certain you are using correct ojdbc driver. Double check if you are actually connecting to the database you are thinking you are. In my case jdbc configuration (in Tomcat/conf) was pointing to different database that had different Oracle version.
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