Copy & Delete Posts < 1.5.8 - Authenticated Arbitrary Post Slug Takeover
The Duplicate Post WordPress plugin before 1.5.8 does not check that a user duplicating a post is allowed to edit it, which, when the slug takeover option is enabled, allows users of a role an administrator has given Duplicate Post WordPress plugin before 1.5.8 access to, such as Contributor, to move any readable post off its permalink and publish their copy at that address.