Zope 2.2.0 through 2.5.1 does not properly verify the access for objects with proxy roles, which could allow some users to access documents in violation of the intended configuration.
http://www.zope.org/Products/Zope/hotfixes/
http://www.securityfocus.com/bid/4229
http://www.redhat.com/support/errata/RHSA-2002-060.html