Comment 31 for bug 1746807

Only one package needs to be downgraded for apt-cdrom to work again: libapt-pkg5.0 to version: libapt-pkg5.0_1.6~alpha5

http://changelogs.ubuntu.com/changelogs/pool/main/a/apt/apt_1.6~alpha7ubuntu1/changelog

Links used for testing:
http://launchpadlibrarian.net/353920547/libapt-pkg5.0_1.6~alpha7_amd64.deb
http://launchpadlibrarian.net/353116448/libapt-pkg5.0_1.6~alpha6_amd64.deb
http://launchpadlibrarian.net/345537288/libapt-pkg5.0_1.6~alpha5_amd64.deb

For each ... I manually "dpkg -i" and then ran "apt-cdrom add".

Results:
libapt-pkg5.0_1.6~alpha7ubuntu1 = fails <-- stock Bionic 20180216
libapt-pkg5.0_1.6~alpha7ubuntu = fails
libapt-pkg5.0_1.6~alpha6 = fails
libapt-pkg5.0_1.6~alpha5 = works <-- Bionic 20180131