The reported vulnerability is a stack buffer overflow in the zbx_snmp_cache_handle_engineid function within the Zabbix server/proxy code. This issue occurs when copying data from session->securityEngineID to local_record.engineid without proper bounds checking.
A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).