mailing list archives
Re: FireWall-1 FTP Server Vulnerability
From: Lars.Troen () MERKANTILDATA NO (Lars.Troen () MERKANTILDATA NO)
Date: Sat, 12 Feb 2000 11:45:30 +0100
From: Check Point Support [mailto:cpsuppor () ts checkpoint com]
Sent: 12. februar 2000 06:01
To: fw-1-mailinglist () lists us checkpoint com
Subject: [FW1] Check Point News Announcement
It has been brought to Check Point's attention that a possible
exists in the control of PASV (passive) FTP connections through
This was developed in a lab environment and requires a specific set of
conditions to have existed, in order to suceed. Check Point has no
of its being used against production environments.
Summary of vulnerability:
FireWall-1's parsing of the FTP control connection was manipulated via
such that a FTP server PASV port number, as processed by FireWall-1, was
associated with the port number of a service with a known security issue
this case, ToolTalk port vulnerability on a un-patched Solaris 2.6
This enabled the client to exploit the server's vulnerability (i.e., an
in.ftpd that returned client-controlled data in an error message and
a possibly unnecessary service: ToolTalk) to gain root access on the
machine. This vulnerability was reported to BugTrag on Wednesday,
9th by John MacDonald of DataProtect.
Minimizing the possible threat:
- Do not enable PASV FTP if not needed.
- Use the FTP Security Server or HTTP security server for PASV FTP
connections to internal FTP servers.
- Those running publicly accessible FTP servers should follow good host
security practices (e.g., not running additional, possibly unnecessary
vulnerable services, keeping up with OS and/or application patches).
- For those using stateful inspection of passive FTP, the following
has been supplied.
The patch consists of a new $FWDIR/lib/base.def file that includes a fix
the problem (the file is compatible with Firewall-1 4.0 SP-5, other
platforms will be released as soon as possible). The fix involves an
enforcement on the existence of the newline character at the end of each
packet on the FTP control connection, this will close off the described
vulnerability. It should be noted that this may cause connectivity
(i.e., blocked FTP connections) in the following scenarios:
1. If FTP control messages larger than the MTU (e.g., large PWD) are
2. If some FTP clients/servers does not put newline at the end of the
3. When passing FWZ encrypted traffic through an intermediate Firewall
The enforcement can be easily disabled by commenting the following line
the base.def file (or by restoring the original base.def file):
Check Point Software Technical Services
- Re: FireWall-1 FTP Server Vulnerability Lars.Troen () MERKANTILDATA NO (Feb 12)