Beginner Guide to IPtables

Hello friends!! In this article we are going to discuss on Iptables and its uses. Iptables is a command-line firewall, installed by default on all official Ubuntu distributions. Using Iptables, you can label a set of rules, that will be go after by the Linux kernel to verify all incoming and outgoing network traffic.

Today we will look at some basic concept of Ipatble using various Iptables options to generate a Filter Table which will filter the incoming and outgoing traffic

Basic Iptables Options

-A :  Add this rule to a rule chain.

-L:  List the current filter rules.

-m conntrack : Allow filter rules to match based on connection state. Permits the use of the --ctstate option.

--ctstate: Define the list of states for the rule to match on. Valid states are:

·         NEW - The connection has not yet been seen.

·         RELATED - The connection is new, but is related to another connection already permitted.

·         ESTABLISHED - The connection is already established.

·         INVALID - The traffic couldn't be identified for some reason.

-m limit: Require the rule to match only a limited number of times. Allows the use of the --limit option.

Useful for limiting logging rules:

·         --limit - The maximum matching rate, given as a number followed by "/second", "/minute", "/hour", or "/day" depending on how often you want the rule to match. If this option is not used and -m limit is used, the default is "3/hour".

-p: Describe the connection protocol used.

--dport :  The destination port(s) required for this rule. A single port may be given, or a range may be given as start: end, which will match all ports from start to end, inclusive.

-j :  Jump to the specified target. By default, iptables allows four targets:

·         ACCEPT - Accept the packet and stop processing rules in this chain.

·         REJECT - Reject the packet and notify the sender that we did so, and stop processing rules in this chain.

·         DROP - Silently ignore the packet, and stop processing rules in this chain.

·         LOG - Log 

-I: Inserts a rule. Takes two options, the chain to insert the rule into, and the rule number it should be.

-I:  INPUT 5 would insert the rule into the INPUT chain and make it the 5th rule in the list.

-s: --source - address [/mask] source specification

-d: --destination - address[/mask] destination specification

Iptables follow Ipchain rules which is nothing but the bunch of firewall rules to control incoming and outgoing traffic

Three Important Types Iptable chains

Input Chain:  Input chain rule rule is used to manage the activities of incoming traffic towards server.

Output Chain: Ouput chain rule is used to manage the activities of outgoing traffic from your server.

Forward Chain: A forward chain rule is used for adding up rules related to forwarding of an ip packet. This is usually used while you have a Linux machine as router linking two networks collectively.

As discribed above by default install iptable is availabe in all Ubuntu distribution but if it is not installed in any Linux based system and you want to install it then excute given below command.

sudo apt-get install iptables

By default iptable is blank which allows all incoming and outgoing connection traffic without filtering them. In order to verify inbuilt rules of iptable we need to execute following command which displays the list of rules if added in iptables.

sudo iptables -L -v

here -L is used for display the chain rules of iptables and  -v for complete information.

Allow Incoming Traffic

In order to allow traffic for any particular port you can use given below command here we have accept incoming on port 22 for SSH, 80 for HTTP and 443for HTTPS respectively

sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPT

sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT

sudo iptables -A INPUT -p tcp --dport 443 -j ACCEPT

So it will allow tcp connection when traffic will coming on port 22, 80 and 443.

Drop/Deny Incoming Traffic

In order to deny traffic for any particular port you can use given below command here we have drop incoming on port 21 for FTP and 23 for Telnet respectively

sudo iptables -A INPUT -p tcp --dport 21 -j DROP

sudo iptables -A INPUT -p tcp --dport 23 -j DROP

So it will deny tcp connection when traffic will coming on port 21, 23 and give a message Time Out. 

Reject Incoming Traffic

Reject and Drop action closely work same in order to obstruct the incoming traffic from establishing connection with server only the difference is that, here it will send message with “ICMP message Port Unreachable” and reject the incoming packet. you can use given below command here we have reject incoming on port 25 for SMTP.

sudo iptables -A INPUT -p tcp --dport 21 -j DROP

So it will reject tcp connection when traffic will coming on port 25 and give a message Destination Port unreachable.

 Allow Incoming Traffic from Specific IP

In order to allow traffic form only a particular IP to establish a secure connection between server and client you can execute given below command

sudo iptables -A INPUT -s 192.168.1.104 -j ACCEPT

It will accept packet coming from network 192.168.1.104

Block Specific Network IP

In order to deny traffic form only a particular IP to establish a secure your server from attacker’s IP you can execute given below command

sudo iptables -A INPUT -s 192.168.1.102 -j DROP

It will deny packet coming from network 192.168.1.102

Block Specific Network Interface

To block a specific network interface, for example eth0, execute given below command which drop the incoming traffic coming from 10.10.10.10

sudo iptables -A INPUT -i eth0 -s 10.10.10.10-j DROP

Here you can change the action to allow traffic from a particular network interface using –j ACCEPT options.

Block Specific IP Range

To block a specific IP range in order to deny, the incoming traffic coming from specific range of IP. Execute given below command which drop incoming packet coming from IP 192.168.1.100 till IP 192.168.1.200

sudo iptables -A INPUT -m iprange --src-range 192.168.1.100-192.168.1.200 -j DROP

Here you can change the action to allow traffic from a particular IP range using –j ACCEPT options.

Block Specific Mac Address

To block a specific Mac address in order to deny, the incoming traffic coming from specific machine. Execute given below command which drop incoming packet coming from given Mac address or attacker machine.

sudo iptables -A INPUT -m mac --mac-source FC:AA:14:6A:9A:A2 -j DROP

Here you can change the action to allow traffic from a particular Mac address using –j ACCEPT options.

BLOCK Ping Request

Network administrator always concern with network security therefore they always Block Ping request either by using Drop or Reject action , here we are blocking Ping request using DROP option as given in below command.

sudo iptables -A INPUT -p icmp -i eth0 -j DROP

View List of Applied Chain rules

In order to view our applied chain rules once again we are going to execute given below command which will dump list of Iptable rules.

sudo iptables -L

From given below image you can observe 4 columns which contains records of IPtable rules.

Here these columns define following information:

Target: Defines applied action

Prot: stand for Protocol type that can TCP, ICMP or UDP

Option: further option to define rule, here it is blank

Source: Incoming traffic network IP Address

Destination: Host IP address which will receive incoming traffic packet.

Now if someone tries to Ping the server machine as shown in given below image, so here you can read the message “Request timed out” which means the server machine has drop our ICMP request packet.

Deleting Any Rule

In order to delete any rule of your Iptable to remove it from inside your filter table you can use option -D with input rule number.  We are going to remove our last rule ICMP drop connection which was at number 12 in the given list of rule.

sudo iptables -D INPUT 12

Here you can replace number 12 from any other number which rule you wish to remove according to your list of rules.

Let’s view our remaining chain rules once again using -L option as done above. From given below image you can observe that now the list contain only 11 rules and eliminated  rule ICMP drop the connection.

Flush IPtables

If you want to remove entire set of rule in order to flush your Iptable then use option -F to flush your ipatble applied rules and execute given below command.

sudo iptables -F

Now once again when we had viewed the list of rule, this time we got empty table as shown in given below image.

Source: https://help.ubuntu.com/community/IptablesHowTo

Payload Processing Rule in Burp suite (Part 2)

Hello friends!! Today we are going to discuss “Payload Encoding” option followed by payload processing of Burpsuite which is advance functionality comes under Intruder Tab for making brute force attack.

Payload Encode
The processing rule can be used to encode the payload using various schemes such as URL, HTML, Base64, ASCII hex or constructed strings.
Let's start!!

First, we have intercepted the request of the login page of the router by giving its default IP which is 192.168.1.1, where we have given an invalid username and password. Then click on login, the burp suite will capture the request of the login page in the intercept tab.

Thus the sent request will be captured by burp suite which you can see in the given below image. In the screenshot I had highlight some value in the last line. Here it tells the type of authentication provided by router is basic and if you have read above theory of basic authentication I had described that it is encoded in base 64

Send the captured request to the Intruder by clicking on the Action Tab and follow given below step. Now open the Intruder tab then select Positions tab and you can observe the highlighted password and follow the given below step for selecting payload position.

·         Press on the Clear button given at right of window frame. 

·          Now select the encoded value of authentication for payload position and click to ADD button on the left side of frame.

·         Choose the Attack type as sniper.

Now click on payloads option after selecting payload position. Then select the Payload type as Simple list, where we have added a dictionary by clicking on Load button. We can either load the dictionary or we can manually add input strings using the Add button in the payload options as shown in the image.

The base64 encoded value of Authentication is combination of username and password now the scenario is to generate same encoded value of authentication with help of user password dictionary, therefore I have made a dictionary.

Before executing the attack we have added a payload processing rule to the payload type which is Encode and we have selected “Base64 encode” scheme because we know router takes the value in Base64.

Select Start Attack in the Intruder menu as shown in the image.

Sit back and relax because this will start brute force attack and try to match string for user authentication. In screenshot you can the status and length of the highlighted value is different from rest of values. This means we can use this encoded value to bypass the user authentication which occur from request number 10. Now check the username and password of 10th line in dictionary. 

And to confirm the username and password matched, we will give the password in the Router's Login Page, which will successfully log us into the Router's Configuration Page. This shows our success in the attack as shown in the image.

Decode
This processing rule can be used to decode the payload using various schemes: URL, HTML, Base64 or ASCII hex. As we know decoding is nothing but reversing the encoding. It can be used in an opposite way in which encoding is carried out.
Hash
This processing rule can be used to carry out a hashing operation on the payload. There are 7 types of hashing algorithms are available in this payload processing rule which is as follows:

·         SHA-384

·         SHA-224

·         SHA-256

·         MD5

·         MD2

·         SHA

·         SHA-512

First, we have intercepted the request of the Redirection Link designed to find redirection vulnerabilities in the LAB created by us and in the hash value of the URL we have given a wrong hash value of HTTP://www.google.com in place of the actual hash value of the HTTP://www.hackingarticles.in in the URL of the redirecting page. We have simply clicked on the Redirection link as shown in the image; the burp suite will capture the request of the redirecting page in the intercept tab.

Send the captured request to the Intruder by clicking on the Action Tab and follow given below step. Now open the Intruder tab then select Positions tab and you can observe the highlighted password and follow the given below step for selecting payload position.

·         Press on the Clear button given at right of window frame. 

·         Now we will select the fields where we want to attack which is the hash value of the redirecting page and then click on Add button.

·         Choose the Attack type as sniper.

Then select the Payload type as Simple list, where we have added a dictionary by clicking on Load button. We can either load the dictionary or we can manually add input strings using the Add button in the payload options as shown in the image.

Before executing the attack we have added a payload processing rule to the payload type which is Hash and then we have selected MD5 which is a commonly used algorithm for converting URL of the websites into a Hash MD5 value. As you can see the input strings of the dictionary are in a simple text form, but this processing rule converts it into Hash MD5 values which can be seen in result window of the attack.

Select Start Attack in the Intruder menu as shown in the image.

Sit back and relax because now the burp suite will do its work, match the Hash MD5 of the Redirecting Page which will give you the correct MD5 value. The moment it will find the correct value, it will change the value of length as shown in the image.

The Hash MD5 value, we will give the Hash value in the URL of the redirecting page which is HTTP://www.hackingarticles.in, which will successfully redirect us to HTTP://www.hackingarticles.in. This shows our success in the attack as shown in the image.

Add Raw Payload
This processing rule can be used to add raw payload value before or after the current processed value. For example it can come in handy whenever we want to submit the same payload in both raw and hashed form.

First, we have intercepted the request of the login page in the Bwapp LAB, where we have given default username and wrong password. Then click on login , the burp suite will capture the request of the login page in the intercept tab.

Send the captured request to the Intruder by right clicking on the space and selecting Send to Intruder option or simply press ctrl + i. Now open the Intruder tab then select Positions tab and the following will be visible. Choose the Attack type as Sniper. Press on the Clear button as shown in the image. Now we will select the fields where we want to attack which is the password and click on Add button.

Send the captured request to the Intruder by clicking on the Action Tab and follow given below step. Now open the Intruder tab then select Positions tab and you can observe the highlighted password and follow the given below step for selecting payload position.

·         Press on the Clear button given at right of window frame. 

·         Now we will select the fields where we want to attack and i.e. the password filed and click on Add button.

·         Choose the Attack type as sniper.

• In the given below image we have selected password that means we will need one dictionary files for password.

Before executing the attack we have added a payload processing rule to the payload type which is Add Raw Payload and then we have selected Append Pre-processed Payload. This adds a raw payload value before and after the current processed value. As you can see the input strings of the dictionary as single input string is repeated twice which can be seen in result window of the attack.
Select Start Attack in the Intruder menu as shown in the image.

Sit back and relax because now the burp suite will do its work, match the password which will give you the correct password. The moment it will find the correct value, it will change the value of length as shown in the image.

And to confirm the password matched, we will give the password in the Bwapp LAB login page, which will successfully log us into the Bwapp lab. This shows our success in the attack as shown in the image.

Skip if Matches Regex
This processing rule can be used to check the current processed value matches a specified regular expression, and if it matches it will skip the payload and will move onto the next one. For example, Suppose we have a parameter value that have a minimum length and want to skip values in the list that are shorter than minimum length defined.
First, we have intercepted the request of the login page in the Bwapp LAB, where we have given default username and wrong password. Then click on login, the burp suite will capture the request of the login page in the intercept tab.

Send the captured request to the Intruder by clicking on the Action Tab and follow given below step. Now open the Intruder tab then select Positions tab and you can observe the highlighted password and follow the given below step for selecting payload position.

·         Press on the Clear button given at right of window frame. 

·         Now we will select the fields where we want to attack and i.e. the password filed and click on Add button.

·         Choose the Attack type as sniper.

• In the given below image we have selected password that means we will need one dictionary files for password.

Then select the Payload type as Simple list, where we have added a dictionary by clicking on Load button. We can either load the dictionary or we can manually add input strings using the Add button in the payload options as shown in the image.

Before executing the attack we have added a payload processing rule to the payload type which is Skip if Matches Regex where we have given an input of {@} in the match regex field. Here we see that as per this rule if the input given matches with any of the input strings in the dictionary it simply skip that value and move on to next.

Now Select Start Attack in the Intruder menu as shown in the image.

Sit back and relax because now the burp suite will do its work, match the password which will give you the correct password. The moment it will find the correct value, it will change the value of length as shown in the image.

Engagement Tools Tutorial in Burp suite

Hello friends!! Today we are going to discuss Importance of Engagement tools which is a Pro-only feature of Burp Suite. It is mainly use in information gathering and hence the analysis of any web application testing.

Its four important utilities are following:

·         Find References

·         Discover Content

·         Schedule Task

·         Generate CSRF POC

Find References

This function can be used to search all Burp suite tools for HTTP responses that link to a particular item. To make use of this function, select an HTTP request anywhere in Burp suite, or any part of the site map, and choose "Find references" in "Engagement tools" in the context menu which can be seen clicking Action Tab within Burp suite.

The result window of the search shows responses (from all Burp tools) that are link to the selected item. Whenever we view an individual search result, the response will be automatically highlighted to show where the linking reference is occurring.

This function treats the original URL as a Prefix whenever we search for links, so if you select a host, you will find all references related to the host and if you select a folder, you will find all references to items inside that folder.

First, we have intercepted the request of the Vulnweb.com which is a demo lab available over the internet which can be used for testing attacks. Then click on enter after writing the URL of the Vulnerable Web in your browser , then the burp suite will capture the request of the web page in the intercept tab.

Then click on Action Tab, after that select the Engagement tools then click on Find References. This will open a result window which will show all the references related to the URL whose request has been captured which is the Vulnerable Web as shown in the image.

Discover Content

This function is used to discover contents and functionality which are not linked with visible content that you can browse or spider.
There are various techniques that burp suite uses to discover content, which includes name guessing, web spidering, and extrapolation from naming conventions observed within the use of application.

Control

This tab shows you the current status of the session. The toggle button represents whether the session is running or not, and it also allows you pause and restart the session.

The following information is displayed about the progress of the discovery session:

• Number of requests made
• Number of bytes transferred in server responses
• Number of network errors
• Number of discovery tasks queued
• Number of spider requests queued
• Number of responses queued for analysis

Target

This option allows you to define or state the start directory of the content discovery session, and whether the files or directories should be targeted. The options that are available are as follows:

• Start directory - This is the location where Burp suite is used to look for content. The items within this path and subdirectories are requested during the session.
• Discover - This option can be used to determine whether the session will look for files or directories or both.

Site Map

The discovery session uses their own site map, showing all of the content which has been discovered within the defined scope. If you have configured your Burp suite to do so, newly discovered items can be added to Burp suite's main site map.

First, we have intercepted the request of the Vulnweb.com which is a demo lab available over the internet which can be used for testing attacks. Then click on enter after writing the URL of the Vulnerable Web in your browser , then the burp suite will capture the request of the web page in the intercept tab.

Then click on Action Tab within the Burp suite, after that select the Engagement tools then click on Content Discovery. This will open a result window which will show the discovery session status and queued tasks which are related to the URL whose request has been captured which is the Vulnerable Web as shown in the image.

Schedule Task

This function can be used to automatically start and stop certain tasks at defined times and intervals. We can use the task scheduler to start and stop certain automated tasks while you are not working, and to save your work periodically or at a specific time.

To make use of this function, select an HTTP request anywhere in Burp suite, or any part of the target site map, and choose "Schedule task" within "Engagement tools" in the context menu which can be seen by clicking right within Burp suite.

The types of task that are available within this function are as follows:

• Scan from a URL
• Pause active scanning
• Resume active scanning
• Spider from a URL
• Pause spidering
• Resume spidering
• Save state

First, we have intercepted the request of the vulnweb.com which is a demo lab available over the internet which can be used for testing attacks. Then click on enter after writing the URL of the Vulnerable Web in your browser , then the burp suite will capture the request of the web page in the intercept tab.

Then click on Action Tab within the Burp suite, after that select the Engagement tools then click on Schedule Task. This will open a window of schedule task options where we have selected Scan from a URL option as shown in the image.

Then Click Next a window will open where we have to give the URL we want to scan its branches from the site map.

Then Click Next we see that the scanner tab of the burp suite is open which scans all the branches beneath the site map of the given URL which is seen in the scan queue tab as shown in the image which are related to the URL whose request has been captured which is the Vulnerable Web as shown in the image.

Generate CSRF PoC

This function can be used to generate a proof-of-concept (PoC) cross-site request forgery (CSRF) attack for any given request.

To access this function, select a URL or HTTP request anywhere in the Burp suite, and choose "Generate CSRF PoC" within "Engagement tools" in the context menu which can be seen by clicking right within Burp suite.

Let's start!!

First, we have intercepted the request of the CSRF (transfer amount) option in the Bwapp LAB, where we have given an Account Number.

 Then click on transfer, the burp suite will capture the request of the page in the intercept tab.

Then click  on Action Tab within the Burp suite, after that select the Engagement tools then click on Generate CSRF PoC. This will open a window of the CSRF PoC where we made a change in Account value and Amount value in CSRF HTML code as shown in the image.

After making changes in the values click on Test in Browser option or Copy HTML this will open the window of Show response in browser then click on COPY, and then paste it in the Browser and Press Enter as shown in the image.

We see a Submit request Button is seen in the browser after that click on it.

It appears to us that the amount is reduced as we have transferred the amount from the account by making changes in the CSRF HTML code as shown in the image.