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Multiple Vendor FTP Bounce Attack Vulnerability
This problem is a design issue with the common implementation of the FTP protocol. In essence, the vulnerability is as follows: when a user FTP's into a host to retrieve files, the connection is two way (i.e. when you log in and request a file, the server then opens a connection back to your host of origin to deliver your requested data). Most FTP servers support what is called 'active mode' which allows users to specify a number of parameters to the FTP daemon. One of these is the PORT command, which lets you specify *where* you would like the return data connection to be sent. Therefore, instead of opening a connection back to yourself to drop off your requested files or data, you can then open that connection back to another host. This is true with both retrieving and putting data. Attackers can exploit this in some instances to circumvent access control, export restrictions, etc. |
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