Magento Open Source 2.2.1, 2.1.10, and 2.0.17 include critical security enhancements and functional updates. Review the release notes for more information: 

Magento Open Source 2.2.1: 
http://devdocs.magento.com/guides/v2.2/release-notes/bk-release-notes.html, 

Magento Open Source 2.1.10: 
http://devdocs.magento.com/guides/v2.1/release-notes/bk-release-notes.html, 

Magento Open Source 2.0.17: 
http://devdocs.magento.com/guides/v2.0/release-notes/bk-release-notes.html  
