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CheckPoint FW1 HTTP Security Hole
From: "Volker Tanger" <volker.tanger () discon de>
Date: Tue, 19 Feb 2002 16:05:22 +0100

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Greetings!

A quite known proxy vulnerability was found for FW1 V4.1 SP5 (plus
hotfixes) - thanks to Ryan Snyder for announcing the first bits on
Firewall-1 mailing list.

If you connect to a server you are allowed to connect to via HTTP
proxy (e.g. a common rule is "Any / WebServer / http->ressource").
Then use the CONNECT method to connect to a different server, e.g.
an internal mailserver.

Example:
        you = 6.6.6.666
        Webserver = 1.1.1.1
        Internal Mailserver = 2.2.2.2

        Rule allows:  Any  Webserver http->ressource

        connect with "telnet 1.1.1.1 80" to the webserver and enter
        CONNECT 2.2.2.2:25 / HTTP/1.0

        response: mail server banner - and running SMTP session e.g.
        to send SPAM from.

You can connect to any TCP port on any machine the firewall
can connect to. Telnet, SMTP, POP, etc.

Restrictions found:
        - connects are only possible if the firewall module
          is allowed access (i.e. via policy/properties,
          specific rules or "Any  (dst) (svc)..." rules
        - you have to allow "CONNECT" - is enabled if you allowed
          "Tunneling" (General tab) connection method or did not
          delete the "*" in "Other" Methods (Match tab)

Fast workarounds:
        - Change your ressource settings to filter out CONNECT
          commands, i.e.
                * disable HTTP tunneling
                * check that "Other" method is specified NOT to
                  match CONNECT (i.e. remove the default wildcard)
        - disallow access from the firewall module (->Properties)
        - replace in all your rules containing the service
          HTTP+Resource this part with plain HTTP. Yes, you loose

          some content security but at least you don't compromise

          your other servers


The thing that really concerns me is, that this general problem has
been known to be an issue with plain HTTP proxies like the Squid since
ages (see e.g. http://www.squid-cache.org/Doc/FAQ/FAQ-10.html#ss10.14).
And why didn't Checkpoint prevent or at least document this?

Puzzled
        Volker

- --

- -------------------------------------------------------------------
volker.tanger () discon de                                 discon GmbH
IT-Security Consulting                           Wrangelstrasse 100
http://www.discon.de/                         10997 Berlin, Germany
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