FTP bounce attack could allow attackers to "proxy" connections
| ftp-bounce (199) |  Medium Risk |
Description:
A normal FTP session occurs by establishing a connection to the FTP control port (TCP port 21). Once this control channel is established, any files to be sent are transferred using a separate connection (the data connection). This is done by the FTP client sending a PORT command containing the IP address and port that it will listen for a TCP connection on. The FTP server then connects back to that port and transfers the file. (There is also a mechanism called Passive FTP whereby the client connects to the server instead, but this method is not involved in this form of attack.) By specifying a different IP address than its own, an FTP client can trick some FTP servers into making a connection and sending data to another host on the network; that host will look like it is being probed or attacked by the FTP server when it fact it is the FTP client that is indirectly attacking it.
This can mask an attacker's identity in attacking a network. It is also possible that an attacker could use this vulnerability to bypass some poorly configured packet filters or firewalls. For example, if the mail server allows telnet connections from an internal FTP server but not from external hosts on the Internet, an attacker may be able to connect to the Telnet port on the SMTP server by "bouncing" through the FTP server.
Consequences:
Gain Access
Remedy:
Upgrade to the latest version of your FTP server, which should include fixes for this problem.
For SGI IRIX:
Upgrade to the latest version of IRIX (6.5.20 or later), or apply the appropriate patch for your system, as listed in SGI Security Advisory 20030304-01-P. See References.
References:
- CERT Advisory CA-1997-27: FTP Bounce.
- Hewlett-Packard Company Security Bulletin HPSBUX9511-028: Security Vulnerability in FTP.
- SGI Security Advisory 20030304-01-P: Multiple Vulnerabilities and Enhancements in ftpd.
- CVE-1999-0017: FTP servers can allow an attacker to connect to arbitrary ports on machines other than the FTP client, aka FTP bounce.
Platforms Affected:
- Apple Mac OS
- Cisco IOS
- Compaq Tru64
- Data General DG/UX
- HP HP-UX
- IBM AIX
- IBM OS2
- IETF FTP
- Linux Kernel
- Microsoft Windows 2000
- Microsoft Windows 2003 Server
- Microsoft Windows 95
- Microsoft Windows 98
- Microsoft Windows 98SE
- Microsoft Windows Me
- Microsoft Windows NT 4.0
- Microsoft Windows XP
- Novell NetWare
- SCO SCO Unix
- SGI IRIX
- Sun Solaris
- WindRiver BSDOS
Reported:
Jul 01, 1997
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