Re: Tool to find hidden web proxy server

From: Javier Fernandez-Sanguino (jfernandez_at_germinus.com)
Date: 09/02/04

  • Next message: Marc: "Re: Tool to find hidden web proxy server" 
    Date: Thu, 02 Sep 2004 15:03:04 +0200
To: vinay mangal <vinay.mangal@eil.co.in>

    vinay mangal wrote:

    > Dear all,
    >
    > Thanks for your suggestions. May be I am not able to define my question
    > properly.
    >
    > This problem is strictly with in company internet access firewall and in the
    > LAN only. In a company, policy for Internet access says it is through IP
    > only. The others can not browse the internet. This policy is implemented on
    > firewall. Few smart guys have installed free proxy server running on non
    > default ports and distributed the internet access to their friends. The
    > firewall sees the traffic coming from the authorized IP and does not stop
    > them. We want to know who has installed proxy on there machine.
    >

    Since you say that the authorised IPs that can browse the Internet are
    a known subset of your company, I suggest you could (in an increasing
    level of complexity):

    - port-scan those systems and determine if there are open ports on
    them that act as a proxy (try using 'nmap -sV'). Of course this will
    not work if they have added a firewall in the system and are blocking
    access to that port to everyone save their friends.

    - analyse the outgoing HTTP traffic through the firewall from those IP
    addresses and look for proxy 'give-aways' in the HTTP headers
    ('X-Forwarded-For:' or 'Via:'). If they have configured the proxy
    server to not print these headers this might not spot out any
    culprits. Use ngrep for this.

    - analyse the outgoing HTTP traffic through the firewall and analyse
    it (you can probably use a lot of accounting tools to extract data
    from tcpdump captures). This will allow you to determine which servers
    are responsible for most of the outgoing HTTP traffic and that might
    be an indication of a proxy in use. You can use ntop for this.

    - access your switches and analyse the traffic statistics of the ports
    used by the IP address that can access the Internet. Ports with a high
    incoming/outgoing byte counts might allow you to distinguish
    legitimate vs. illegitimate accesses. Most clients (if only used for
    browsing) will generate a high incoming byte count but a low outgoing
    byte cout so a high outgoing byte count might be an indication of
    traffic being proxied to other clients.

    - (if your switches permit) use traffic monitoring (port spanning) or
    netflows to do accounting on communications between the different IP
    address of your local company, discard known servers and analyse the
    traffic to detect uncommon client-server relationships that generate
    an uncommon ammount traffic. In most office environments you should
    only see traffic going from clients to known servers (or to the
    Internet) as there is rarely a need for clients to communicate amongst
    themselves (unless sharing resources). That could allow you to detect
    both the IP addresses of illegitimate servers and the IP addresses of
    those using them. You can use ntop for this.

    Good luck.

    Javier

    PS: You basicly need tools to do traffic analysis, but you first have
    to place yourself in a position in which you know what you want to
    capture, and how to analyse it to obtain your rogue users so before
    thinking about tools, think about how to capture that data you need.

    ------------------------------------------------------------------------------
    Ethical Hacking at the InfoSec Institute. All of our class sizes are
    guaranteed to be 12 students or less to facilitate one-on-one interaction
    with one of our expert instructors. Check out our Advanced Hacking course,
    learn to write exploits and attack security infrastructure. Attend a course
    taught by an expert instructor with years of in-the-field pen testing
    experience in our state of the art hacking lab. Master the skills of an
    Ethical Hacker to better assess the security of your organization.

    http://www.infosecinstitute.com/courses/ethical_hacking_training.html
    -------------------------------------------------------------------------------

  • Next message: Marc: "Re: Tool to find hidden web proxy server"

    Relevant Pages

    • Re: All Domain Admin Accounts Locked
      ... There are no ports open to this server from the firewall/router. ... Web servers with ports 80 and 443 open. ... One other thing I want to mention is that the event logs show attempts ... These attempts must be coming from the internet, ...
      (microsoft.public.win2000.security)
    • Add new Exchange server behind a firewall to existing site
      ... We have an existing Exchange system that consists on three Exchange ... The Exchange servers have been installed as a single Exchange site even ... What ports do we need to open if I install the server ... I am planning to route Internet email directly to/from the new email ...
      (microsoft.public.exchange.connectivity)
    • Add new Exchange server behind a firewall to existing site
      ... We have an existing Exchange system that consists on three Exchange ... The Exchange servers have been installed as a single Exchange site even ... What ports do we need to open if I install the server ... I am planning to route Internet email directly to/from the new email ...
      (microsoft.public.exchange.connectivity)
    • Re: the naked router
      ... >respectively nntp (news servers). ... >couldn't use your browser on the internet or connect to newsgroups. ... Those ports are used to initiate connections to servers on the ...
      (comp.security.firewalls)
    • RE: IIS6 Security and other web servers
      ... IIS6 Security and other web servers ... I know of no Windows architecture that is exposed directly to ... I know of a number of LAMP-type servers that are ... exposed directly to the Internet with no intervening layers. ...
      (Security-Basics)