-----Original Message----- From: Check Point Support [mailto:cpsupporat_private] Sent: 12. februar 2000 06:01 To: fw-1-mailinglistat_private Subject: [FW1] Check Point News Announcement News Announcement: http://www.checkpoint.com/techsupport/alerts/pasvftp.html It has been brought to Check Point's attention that a possible vulnerability exists in the control of PASV (passive) FTP connections through FireWall-1. 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 knowledge of its being used against production environments. Summary of vulnerability: FireWall-1's parsing of the FTP control connection was manipulated via MTU 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 (in this case, ToolTalk port vulnerability on a un-patched Solaris 2.6 system). 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 running a possibly unnecessary service: ToolTalk) to gain root access on the machine. This vulnerability was reported to BugTrag on Wednesday, February 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 and vulnerable services, keeping up with OS and/or application patches). - For those using stateful inspection of passive FTP, the following patch has been supplied. Patch: The patch consists of a new $FWDIR/lib/base.def file that includes a fix to 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 problems (i.e., blocked FTP connections) in the following scenarios: 1. If FTP control messages larger than the MTU (e.g., large PWD) are exchanged. 2. If some FTP clients/servers does not put newline at the end of the line. 3. When passing FWZ encrypted traffic through an intermediate Firewall gateway. The enforcement can be easily disabled by commenting the following line in the base.def file (or by restoring the original base.def file): #define FTP_ENFORCE_NL Thank you, Check Point Software Technical Services
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