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From: Jochen Bauer (jtbinside-security.de)
Date: Mon Jul 09 2001 - 07:01:46 CDT

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    FOR PUBLIC RELEASE

    ------------------------------------------------------------------------
    Inside Security GmbH Vulnerability Notification
    Revision 1.2 2001-07-09
    ------------------------------------------------------------------------

    The latest version of this document is available at
    http://www.inside-security.de/advisories/fw1_rdp.html

    -----------------------------------------------
    Check Point FireWall-1 RDP Bypass Vulnerability
    -----------------------------------------------

    Summary:
      It is possible to bypass FireWall-1 with faked RDP packets
      if the default implied rules are being used.

      RDP (Reliable Data Protocol, specified in RFC 908) is used by
      FireWall-1 on top of the User Datagram Protocol (UDP) to establish
      encrypted sessions.

      FireWall-1 management rules allow arbitrary eitherbound RDP connections
      to traverse the firewall. Only the destination port (259) and the RDP
      command are verified by FireWall-1. By adding a faked RDP header to normal
      UDP traffic any content can be passed to port 259 on any remote host on
      either side of the firewall.

      Implied rules can't be easily modified or removed (except all together)
      with the FireWall-1 policy editor.

    Impact:
      Given access to hosts on both sides of a firewall a tunnel to bypass
      the firewall could be built using this vulnerability. Such access
      could be gained with a trojan horse that uses this vulnerability to
      connect from the inside back to the machine of the attacker. But also
      arbitrary connections from the outside to machines behind the firewall
      (even if they are supposedly totally blocked from the in- and outside
      by the firewall) can be established, for example to communicate with
      infiltrated programs like viruses.

    Affected systems:
      Check Point VPN-1(TM) & FireWall-1(R) Version 4.1

    Releases tested:
      Build 41439 [VPN + DES]
      Build 41439 [VPN + DES + STRONG]
      Build 41716 [VPN + DES + STRONG] (SP2)

    Vendor status:
      The vulnerability has been reported to Check Point and a fix is
      scheduled for today. We want to thank Check Point Software Technologies
      for their quick reaction.

    Detailed description:
      As FireWall-1 rulesets are created they are translated into the INSPECT
      language (similar to C) and by default include the file $FWDIR/lib/base.def
      which itself includes $FWDIR/lib/crypt.def in line 259. Together they define
      protocol names and the so called implied rules (for FireWall-1 management).
      In line 62 the macro accept_fw1_rdp is defined to accept any eitherbound
      connection that matches the following characteristics:
        - Protocol UDP
        - Destination port 259 (RDP)
        - RDP Command RDPCRYPTCMD (100), RDPCRYPT_RESTARTCMD (101),
          RDPUSERCMD (150) or RDPSTATUSCMD (128).
      The RDP command types RDPCRYPT = {RDPCRYPTCMD,RDPUSERCMD,RDPSTATUSCMD}
      and RDPCRYPT_RESTART = {RDPCRYPT_RESTARTCMD} will permit traversal of
      faked RDP packets (regardless of the value of NO_ENCRYPTION_FEATURES,
      undefined by default).

    Proof of concept code:
      Proof of concept code has been submitted to Check Point. We are planning
      to make this code publicly available within a few days.

    Suggested workarounds:
      - Comment line 2646 of crypt.def ( accept_fw1_rdp; )
      - Deactivate implied rules in the Check Point policy editor (and build
        your own rules for management connections).
      - Block UDP traffic to port 259 on your perimeter router.

    Credits:
      This vulnerability was found and documented by Jochen Thomas Bauer
      <jtbinside-security.de> and Boris Wesslowski <bwinside-security.de>
      of Inside Security GmbH, Stuttgart, Germany.

    ------------------------------------------------------------------------
    (C) 2001 Inside Security GmbH
    This notice may be redistributed freely provided that redistributed copies
    are complete and unmodified, and include all date and version information.

    ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES,
    INCLUDING ANY WARRANTY OF NON-INFRINGEMENT OR IMPLIED WARRANTY OF
    MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE HEREBY DISCLAIMED
    AND EXCLUDED TO THE EXTENT ALLOWED BY APPLICABLE LAW.

    IN NO EVENT WILL INSIDE SECURITY GMBH BE LIABLE FOR ANY LOST REVENUE,
    PROFIT OR DATA, OR FOR DIRECT, SPECIAL, INDIRECT, CONSEQUENTIAL, INCIDENTAL
    OR PUNITIVE DAMAGES HOWEVER CAUSED AND REGARDLESS OF ANY THEORY OF
    LIABILITY ARISING OUT OF THE USE OF OR INABILITY TO USE THE INFORMATION
    CONTAINED IN THIS SECURITY BULLETIN, EVEN IF INSIDE SECURITY GMBH HAS
    BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

    If any of the above provisions are held to be in violation of applicable
    law, void, or unenforceable in any jurisdiction, then such provisions are
    waived to the extent necessary for this disclaimer to be otherwise
    enforceable in such jurisdiction.
    ------------------------------------------------------------------------