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NTA discover Raptor Firewall vulnerability

NTA discover Raptor Firewall vulnerability

NTA Monitor has discovered a vulnerability in the latest version of the Raptor Firewall, 6.5.3i operating on Sun Solaris. The flaw can make an FTP server behind the Firewall vulnerable to the well-known FTP bounce attack even if the FTP server is itself not vulnerable to this issue.

NTA Monitor discovered the issue in the course of a Regular Monitor penetration test performed for a corporate client. NTA's test report detailed the system's vulnerability to the FTP bounce attack, which upon further investigation was found to be caused by the Firewall rather than the FTP server . See packet traces below.

tcpdump packet trace - hacker system tcpdump packet trace - ftp server tcpdump packet trace- victim system

The FTP bounce attack, involves a hostile client system connecting to an FTP server and tricking it into sending data to a 3rd party system, the "victim" rather than back to the connecting client. Most modern FTP servers safeguard against this well known problem, by preventing a client from specifying an IP address, other than the one used to connect.

The Raptor issue occurs when the Firewall FTP proxy is used for inbound FTP connections. When handing connections to the FTP server, the Firewall proxy re-writes the IP address in the FTP PORT command, in such a way that it appears to specify the connecting client's IP address. This occurs even if the IP address in the PORT command specifies a victim system. When the FTP server sends data to this port, the Firewall changes the address back to that of the victim on the way out.

[diagram]

The FTP server has no way of detecting the FTP bounce attack because the addresses are rewritten so that they appear to reference the client system. It will therefore unknowingly send data to a victim system if requested by a hostile client.

This is a rare example of a Firewall increasing the vulnerability of a system. In the worst case, the Frewall may provide an inadequate level of defence but a Firewall should never have a detrimental effect on security.

The primary implication of this vulnerability, is the ability for a hacker to use an organisation's system as a vehicle to attack a victim system, whilst completely hiding their identity. Possible attacks include port scanning and sending of unsolicited data to arbitrary ports on the victim system.

The vulnerability has been posted on Bugtraq http://online.securityfocus.com/archive/1/267784

NTA Monitor are offering a specific test to check for vulnerability to this flaw visit here for more information.

This advisory was first released on 30th January 2003.