Cisco Dial NMS Implementation Manual page 21

SNMP lacks authentication capabilities, which results in a variety of security threats:
Masquerading—An unauthorized entity attempting to perform management operations by
assuming the identity of an authorized management entity.
Modification of information—An unauthorized entity attempting to alter a message generated by
an authorized entity, so the message results in unauthorized accounting management or
configuration management operations.
Message sequence and timing modifications—Occurs when an unauthorized entity reorders,
delays, or copies and later replays a message generated by an authorized entity.
Disclosure—Results when an unauthorized entity extracts values stored in managed objects.
The entity can also learn of notifiable events by monitoring exchanges between managers and
agents.
Because SNMP does not implement authentication, many vendors do not implement Set
operations, which reduce SNMP to a monitoring facility.