Vixie Cron is a command scheduler with extended syntax over cron.
Roman Veretelnikov discovered that Vixie Cron fails to properly check whether it can drop privileges accordingly if setuid() in do_command.c fails due to a user exceeding assigned resource limits.
Local users can execute code with root privileges by deliberately exceeding their assigned resource limits and then starting a command through Vixie Cron. This requires resource limits to be in place on the machine.
There is no known workaround at this time.
All Vixie Cron users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=sys-process/vixie-cron-4.1-r9"