There are several projects that are exceptions:
- Wikinews projects are licensed under CC BY 2.5 only (according to configuration of wgRightsUrl).
- Hungarian Wikinews is licensed under CC BY 3.0 only (according to the same).
- Wikidata is licensed under CC BY-SA 3.0 only (according to configuration of wgRightsPage).
There are also several kinds of content that are exceptions:
- Content of Wikidata main namespace, Property, Lexeme and EntitySchema namespaces is available under CC0 (https://www.wikidata.org/wiki/Wikidata:Copyright)
- Content of Wikimedia Commons structured data about files is available under CC0 (I'm struggling to find a page that clearly documents this…)
- Content of MediaWiki.org help namespace is available under CC0 (https://www.mediawiki.org/wiki/Project:PD_help)
- Files uploaded to all wikis are available under a variety of licenses, as specified in each file's description
- Tabular data and map data on Wikimedia Commons in the Data namespace is also available under a variety of licenses. Each piece of content documents this with the license attribute (by default CC0).
- (there may be others)