CEH-001 Exam Dumps : Certified Ethical Hacker (CEH)

A penetration tester is conducting a port scan on a specific host. The tester found several ports opened that were confusing in concluding the Operating System (OS) version installed. Considering the NMAP result below, which of the following is likely to be installed on the target machine by the OS?

Starting NMAP 5.21 at 2011-03-15 11:06

NMAP scan report for 172.16.40.65

Host is up (1.00s latency).

Not shown: 993 closed ports

PORT STATE SERVICE

21/tcp open ftp

23/tcp open telnet

80/tcp open http

139/tcp open netbios-ssn

515/tcp open

631/tcp open ipp

9100/tcp open

MAC Address: 00:00:48:0D:EE:89

When a normal TCP connection starts, a destination host receives a SYN (synchronize/start) packet from a source host and sends back a SYN/ACK (synchronize acknowledge). The destination host must then hear an ACK (acknowledge) of the SYN/ACK before the connection is established. This is referred to as the "TCP three-way handshake." While waiting for the ACK to the SYN ACK, a connection queue of finite size on the destination host keeps track of connections waiting to be completed. This queue typically empties quickly since the ACK is expected to arrive a few milliseconds after the SYN ACK. How would an attacker exploit this design by launching TCP SYN attack?

An attacker is attempting to telnet into a corporation's system in the DMZ. The attacker doesn't want to get caught and is spoofing his IP address. After numerous tries he remains unsuccessful in connecting to the system. The attacker rechecks that the target system is actually listening on Port 23 and he verifies it with both nmap and hping2. He is still unable to connect to the target system. What could be the reason?