In cryptography, a brute force attack is a strategy used to break the encryption of data. It involves traversing the search space of possible keys until the correct key is found.
The selection of an appropriate key length depends on the practical feasibility of performing a brute force attack. By obfuscating the data to be encoded, brute force attacks are made less effective as it is more difficult to determine when one has succeeded in breaking the code.
In the context of network security, a spoofing attack is a situation in which one person or program successfully masquerades as another by falsifying data and thereby gaining an illegitimate advantage.
FTP bounce attack is an exploit of the FTP protocol whereby an attacker is able to use the PORT command to request access to ports indirectly through the use of the victim machine as a middle man for the request.
This technique can be used to port scan hosts discreetly, and to access specific ports that the attacker cannot access through a direct connection.
nmap is a port scanner that can utilize an FTP bounce attack to scan other servers.
The representation of the IP addresses and port numbers in the PORT command and PASV reply poses a challenge to FTP in traversing Network address translators (NAT). The NAT device must alter these values, so that they contain the IP address of the NAT ed client, and a port chosen by the NAT device for the data connection. The new address and port will probably differ in length in their decimal representation from the original address and port. Such translation is not usually performed in most NAT devices, but special application layer gateways exist for this purpose.
Where FTP access is restricted, a remote FTP or FTPmail service can be used to circumvent the problem. An email containing the FTP commands to be performed is sent to a remote FTP server, which is a mail server that parses the incoming email, executes the FTP commands, and sends back an email with any downloaded files as an attachment. Obviously this is less flexible than an FTP client, as it is not possible to view directories interactively or to modify commands, and there can also be problems with large file attachments in the response not getting through mail servers. As most internet users these days have ready access to FTP, this procedure is no longer in everyday use.
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