D-Bus is a message bus system which processes can use to talk to each other.
It was discovered that D-Bus did not properly handle the situation when two usernames have the same numeric UID.
An attacker could possibly cause a Denial of Service condition or trigger other undefined behavior, possibly including incorrect authorization decisions.
There is no known workaround at this time.
All D-Bus users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=sys-apps/dbus-1.12.20"