In which of the following scanning techniques does a scanner connect to an FTP server and request that server to start data transfer to the third system?

Question

Options

• AXmas Tree scanning
• BTCP FIN scanning
• CTCP SYN scanning
• DBounce attack scanning

• A
  15% (7)
• B
  8% (4)
• C
  4% (2)
• D
  73% (35)

Explanation

In the TCP FTP proxy (bounce attack) scanning, a scanner connects to an FTP server and requests that server to start data transfer to the third system. Now, the scanner uses the PORT FTP command to declare whether or not the data transfer process is listening to the target system at the certain port number. Then the scanner uses LIST FTP command to list the current directory. This result is sent over the server. If the data transfer is successful, it is clear that the port is open. If the port is closed, the attacker receives the connection refused ICMP error Answer: A is incorrect. Xmas Tree scanning is just the opposite of null scanning. In Xmas Tree scanning, all packets are turned on. If the target port is open, the service running on the target port discards the packets without any reply. According to RFC 793, if the port is closed, the remote system replies with the RST packet. Active monitoring of all incoming packets can help system network administrators detect an Xmas Tree scan. Answer: B is incorrect. TCP FIN scanning is a type of stealth scanning, through which the attacker sends a FIN packet to the target port. If the port is closed, the victim assumes that this packet was sent mistakenly by the attacker and sends the RST packet to the attacker. If the port is open, the FIN packet will be ignored and the port will drop that packet. TCP FIN scanning is useful only for identifying ports of non Windows operating system because Windows operating systems send only RST packets irrespective of whether the port is open or closed. Answer: C is incorrect. TCP SYN scanning is also known as half-open scanning because in this a full TCP connection is never opened. The steps of TCP SYN scanning are as follows: 1.The attacker sends SYN packet to the target port. 2.If the port is open, the attacker receives SYN/ACK message. 3.Now the attacker breaks the connection by sending an RST packet. 4.If the RST packet is received, it indicates that the port is closed. This type of scanning is hard to trace because the attacker never establishes a full 3-way handshake connection and most sites do not create a log of incomplete TCP connections.

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