libvirt is a C toolkit for manipulating virtual machines.
A file descriptor for /dev/mapper/control was insufficiently protected.
A local attacker may be able to escalate to root privileges.
There is no known workaround at this time.
All libvirt users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=app-emulation/libvirt-6.7.0"