Portage is the package management and distribution system for Gentoo.
Portage does not verify X.509 SSL certificates properly if HTTPS is used.
A remote attacker can spoof servers and modify binary package lists via specially crafted certificates.
There is no known workaround at this time.
All Portage users should upgrade to the latest version:
# emerge --sync # emerge --ask --oneshot --verbose ">=sys-apps/portage-18.104.22.168"