The zabbix sender protocol allows sending huge amouts of data (64 bit integer). If you submit a large amount, the servers stops reading data at 1GB and causes 100% CPU load. This can be used to generate a denial of service and crash the server:
26372:20120730:175909.834 file:str.c,line:204 zbx_realloc: out of memory. Requested 1073741824 bytes.