SNMP Lab Setup and Penetration Testing

What is SNMP?

Simple Network Management Protocol (SNMP) is a protocol for network management. It is used for collecting information from, and configuring, network devices, such as servers, printers, hubs, switches, and routers on an Internet Protocol (IP) network. It usually run on UDP port 161.

Download Vyos Link: https://downloads.vyos.io/?dir=release/1.1.8

Create New Virtual Machine using the VMware and change the Network Adapter to Bridged as shown in the given screenshot.

After completing the initial setup in the VMware Boot the Newly created Virtual Machine by clicking on the Power on the Virtual Machine.

The Default Login Credentials for Vyos are

Username: vyos

Password: vyos

The Initial Boot of Vyos will be as shown below:

This is a Live Boot of the vyos, so we will install the vyos to use it properly.

We will use the iso image to install vyos. Type the following command:

Enter “Yes” where it asks to continue.

Next it will ask about the partition management.

Enter “Auto” where it asks about Partition.

It will detect the drives in the Virtual System and ask you to select the particular drive in which you want to install vyos.

Enter “sda” where it asks about the location for installation.

Next it will ask about the size for the root partition for the vyos.

You can enter any size from 1000MB to 21474MB. But it is recommended to keep it maximum i.e. 21474MB.

Next it will ask about the name for the image.

By default the name is set to the version number that is 1.1.8. You can either give a personalised name or you can leave it default.

Next it will ask about the location to copy the sda.

It is recommended to keep it default.

After that it will ask for the password to be kept for the administrator account.

By default it is kept vyos. But from security point of view it is recommended to change it to something complex which is difficult to guess or brute force.

Now it will ask for the drive on which you want to setup GRUB Boot-loader? Again leave it default to “sda”.

After that we have completed the vyos setup. Reboot using the command

After reboot it will ask for login credentials, Enter the credential that you entered during the installation.

Now we will configure the Network Interface. To do that, we will have to enter configuration mode.

After entering into configuration mode set up Network interface

Syntax: set interface ethernet [network interface] address [Static IPv4 Address]

Now Commit and Save the Configuration

After that type “exit” to get out of configuration mode and then reboot the machine using “reboot” command

We are rebooting because the configuration changes come in effect only after a reboot.

You can the view interface which we configured by using the command

Note: Above command will run in configuration mode.

Start SNMP service

Now we will set up the snmp service in the Vyos.

For that we will enter configuration mode using command

Now to set up a snmp service we will need to add a community string and give it an authorization. To do that:

Syntax: set service snmp community [community-string] authorization [auth-mode]

[community-string]: It can be anything but normally it is either public or private. But from a security point of view it is recommended to keep it that cannot be easily guessed or bruteforced.

[auth-mode]: It is the Authorization Mode. We have two options

  1. [ro]: Read Only Authorization (It can only be used to read or extract data, we can change it using this string)
  2. [rw]: Read Write Authorization (It can be used to change the data using the string)

Now let’s set a user for the system.

Firstly Enter the Configuration Mode.

Now to add a user we will use the following command,

Syntax: set system login user [username] authentication plaintext-password [password]

After this commit the configuration and save it. Also reboot the machine so that changes may take effect.

We have successfully completed snmp Lab in Vyos.

SNMP Enumeration using Kali Linux

Now that we have setup a snmp service let’s pentest it through kali linux inbuilt tools one by one, where We can read and extract information using the community string that have the authorization of reading only but to change the information we will have to use the community string with the read and write authorization.

Nmap

Let’s check using nmap in Kali Linux Machine which is running on the same network.

[-sU]: UDP Ports as SNMP service runs on UDP port

[-p]: Specify Port Number; SNMP service runs on port 161 and 162

From given below image you can observed that it has also shown port 161 is open.

Snmpwalk

snmpwalk is an SNMP application that uses SNMP GETNEXT requests to query a network entity for a tree of information.

Here

[-v1]: Level of verbose mode

[-c]: Community String

From given below image you can observe all details that are specified for “STRING”

Snmpwalk

We can manipulate these details using the iso id, using another tool snmpset. Here we are renaming the host string from vyos to hacked

Let’s check if the changes we implemented had an effect using snmpwalk

As you can see that the we have successfully change the host name from vyos to hacked.

We can extract a number of information using snmpwalk

As the data extracted by snmp walk is quite large we can extract that into a text file by using command below

We can use gedit to view the extracted information

SNMP-Check

Like to snmpwalk, snmp-check allows you to enumerate the SNMP devices and places the output in a very human readable friendly format. It could be useful for penetration testing or systems monitoring.

Here,

[-p]: To specify port

[-c]: To specify Community String

Braa

Braa is a mass snmp scanner. The intended usage of such a tool is of course making SNMP queries – but unlike snmpwalk from net-snmp, it is able to query dozens or hundreds of hosts simultaneously, and in a single process. Thus, it consumes very few system resources and does the scanning VERY fast.

Braa implements its OWN snmp stack, so it does NOT need any SNMP libraries like net-snmp.

Syntax: braa [Community-string]@[IP of SNMP server]:[iso id]

Metasploit

We can enumerate SNMP using a Metasploit module called snmp_enum.

We have fetched same result from metasploit as above.

Author: Pavandeep Singh is a Technical Writer, Researcher and Penetration Tester Contact here

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