Is my firewall stateful or stateless?
Stateful firewalls are capable of monitoring and detecting states of all traffic on a network to track and defend based on traffic patterns and flows. Stateless firewalls, however, only focus on individual packets, using preset rules to filter traffic.
What is ACK scan nmap?
It is used to map out firewall rulesets, determining whether they are stateful or not and which ports are filtered. ACK scan is enabled by specifying the -sA option. When scanning unfiltered systems, open and closed ports will both return a RST packet.
What happens when Nmap is blocked by a firewall?
When firewalling is not involved, virtually all systems respond with an ICMP port unreachable when Nmap probes a closed port. Open ports usually do not respond at all. So if a deny-by-default firewall drops a probe packet, Nmap cannot tell if the port is open or filtered. Retransmissions do not help here, as the port will never respond.
Why does Nmap scan only show open ports?
In the section called “ACK Scan”, SYN and ACK scans were run against a machine named Para. The SYN scan showed only two open ports, perhaps due to firewall restrictions. Meanwhile, the ACK scan is unable to recognize open ports from closed ones. Example 10.6 shows another scan attempt against Para, this time using a FIN scan.
Are there any scanning techniques that bypass firewall rules?
Many other scan types are worth trying, since the target firewall rules and target host type determine which techniques will work. Some particularly valuable scan types are FIN, Maimon, Window, SYN/FIN, and NULL scans. These are all described in Chapter 5, Port Scanning Techniques and Algorithms.
Which is more secure a stateful firewall or ACK scan?
These stateful firewalls are usually more secure because they can be more restrictive. Blocking ACK scans is one extra available restriction. The downsides are that they require more resources to function, and a stateful firewall reboot can cause a device to lose state and terminate all established connections passing through it.