On December 8th, 2015 the Plone Security Team released a hotfix for an issue related to unauthorized disclosure of registered user information.
PLONE VERSIONS SUPPORTED
This patch is compatible with all supported Plone versions (i.e. Plone 4, Plone 5). It may work on earlier versions of Plone, but as these are officially unsupported they have not undergone the same level of testing with the patch.