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CERT Coordination Center

Check Point FireWall-1 allows fragmented packets through firewall if Fast Mode is enabled

Vulnerability Note VU#446689

Original Release Date: 2001-01-05 | Last Revised: 2001-08-30


If any rules include the "Fast Mode" option, Check Point Firewall-1 and VPN-1 will incorrectly allow unauthorized connection attempts to hosts that should be restricted.


A feature called "Fast Mode" (or "FASTPATH"), included in Check Point FireWall-1 and VPN-1 is designed to improve performance in older versions of these products. Unfortunately, a system with this feature enabled in any rules may not adequately protect systems from specially malformed TCP fragment packets. The Fast Mode feature is disabled by default. Specifically, an intruder can make unauthorized connection attempts to hosts they know the IP address for.

More information about this vulnerability is available from Check Point's web site:

The "Fast Mode" feature is scheduled to be discontinued in the next release of the Check Point FireWall-1 and VPN-1 products.


An intruder who knows the IP address of a protected host can make unauthorized connection attempts to the host.


Upgrade your product to version 4.1-SP3 or 4.0-SP8.

Turn off "Fast Mode" in all rule sets. This change is not needed if you upgrade to 4.1-SP3 or 4.0-SP8.

Vendor Information


Check Point Affected

Notified:  January 05, 2001 Updated: February 06, 2001



Vendor Statement

Not all hosts protected by the firewall are vulnerable, only a specific subset:

    • hosts used in the "Destination" column of a rule utilizing Fastmode, or
    • hosts at least one router hop away from the firewall
Also, the hosts must be reachable/routable from the attacker's side of the firewall; ie, in order for a host to be vulnerable, either no address translation or static (1-to-1) address translation must be used for that hosts. In a network using RFC 1918 addresses, where all outbound hosts hide behind a single IP address, none of the protected hosts would be vulnerable.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.


The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

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The information contained in this vulnerability note was obtained from the Check Point security advisory on this topic.

This document was written by Cory F Cohen.

Other Information

CVE IDs: None
Severity Metric: 26.04
Date Public: 2000-12-19
Date First Published: 2001-01-05
Date Last Updated: 2001-08-30 15:42 UTC
Document Revision: 8

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