Trying to import an XML backup into Confluence, we might have the below issue:

Import failed. Check your server logs for more information. com.atlassian.confluence.importexport.ImportExportException: Unable to complete import: An invalid XML character (Unicode: 0xffff) was found in the CDATA section.

Couldn't find the specific steps to reproduce it but certain XML backups have this issue. This has including been documented here.

This looks like a issue with the entities.xml file, and can be fixed by running the below command on Terminal:

perl -i -pe 's/\xef\xbf\xbf//g' entities.xml

Notes

The attached space export file was manually modified to add the invalid \xFFFF character into entities.xml. Entering the character through the editor is not possible.