XWiki is a generic wiki platform. In XWiki Platform versions 10.9 through 16.4.6, 16.5.0-rc-1 through 16.10.2, and 17.0.0-rc-1, the title of every single page whose reference is known can be accessed through the REST API as long as an XClass with a page property is accessible, this is the default for an XWiki installation. This allows an attacker to get titles of pages whose reference is known, one title per request. This doesnt affect fully private wikis as the REST endpoint checks access rights on the XClass definition. The impact on confidentiality depends on the strategy for page names. By default, page names match the title, so the impact should be low but if page names are intentionally obfuscated because the titles are sensitive, the impact could be high. This has been fixed in XWiki 16.4.7, 16.10.3 and 17.0.0 by adding access control checks before getting the title of any page.
The code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor.