It appears to use capabilities:

  $ ps u 561
  USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
  ntp        561  0.0  0.0   5856   780 ?        Ss   Jul14  22:37 /usr/sbin/ntpd -p /var/run/ntpd.pid -g -u 103:107

  $ /sbin/getpcaps 561
  Capabilities for `561': = cap_net_bind_service,cap_sys_time+ep