Please update your forum profile with a real handle instead of "9ab3256b-d8ca-4a0a-9a9a-e37d01668fe6".
All the instructions I've seen reference downloading and installing the patchset from support.oracle.com if installing atop of an existing 4.x environment. Can someone tell me where to get the patch 17966818 if I do not have an Oracle support identifier?
Patch releases that can be applied to existing instances are only available to customers with Oracle Support.
Upgrading a 4.2.x installation to 4.2.5 using the full apex_4.2.5.zip OTN download requires all workspaces and applications to be backed up, APEX 4.2.x to be uninstalled, performing a clean 4.2.5 installation, and restoring the backed up metadata.