Debian is a free Operating System for your laptop, server or embedded device. But it provides more than a pure OS: it comes with over 59000 packages, with a Long Term Support cycle reaching 5 years for each stable release.
Besides stable releases, Debian also provides a testing distribution channel, which is daily updated with the latest and greatest opensource software. Debian strives for correctness of implementation, as detailed in the official Debian Policy, and compliance to Free and Opensource software licensing, as documented in the Debian Free Software Guidelines.
The Vagrant boxes available here for download are maintained by Debian Developers but are not yet an official part of the Debian project.
The contrib-* boxes include components outside the main archive: namely the vboxfs kernel module for shared folders.
see https://www.debian.org/Bugs/Reporting and report the bug against the virtual package cloud.debian.org