Wifi Hacking with aircrack-ng
Introduction
This post is essentially a re-write of notes I took around 2 years ago. Learning to use aircrack-ng and break into my own router was both fun but also a bit shocking as to how easily someone could do this. The difficult part is guessing the password to a router due to processing power needed, but sniffing wifi networks is a trivial process.
There are other methods of doing this as well. In fact, I discovered bettercap earlier this year and it is easy to use. Perhaps I’ll write a post using that tool in the future.
I used Kali Linux for the entire process, but the process should be very similar for any Linux distribution. aircrack-ng is already included on Kali Linux but you can install it on any Linux OS.
Disclaimer: This is purely for educational purposes. Do not try to break into access points that do not belong to you.
What is aircrack-ng?
As described on the official aircrack-ng website, aircrack-ng is a complete suite of tools to assess WiFi network security. It can be used to scan wifi signals and to perform denial-of-service (DOS) attacks.
The goal in this post is to use the tools included in aircrack-ng to:
- Scan for nearby routers
- Send spoofed deauthentication packets on behalf of a connected client
- Capture the 4-way handshake hash
- Crack the hash, which reveals the password of the router in plaintext
Hardware requirements
To use aircrack-ng you’ll need a wireless network adapter that has monitor mode and packet injection capabilities. Feel free to do some research about your particular card and it’s compatibility. There’s a good guide on the aircrack-ng site that can help you with research. You can also do what I did and buy a cheap USB wireless adapter with these capabilities. I have the Panda Wireless N600 and it works perfectly fine on my Macbook Pro.
Installation
If you’re not on Kali Linux, aircrack-ng is most likely available through your preferred package manager. For Windows users, refer to the official aircrack-ng site to download the suite.
Setting up monitor mode
We’ll need to set up monitor mode in our wireless network adapter. Monitor mode allows the wireless network interface to capture all wireless traffic. This means we’ll be able to see nearby wireless access points and devices connected to each one.
To set the network adapter to monitor mode, first find the name of the interface as your system detects it. You can see this using ifconfig. In my case, the interface name of my USB wireless adapter is wlan0. I can set it to monitor mode using the following commands:
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Now, we need to check that no processes interfere with the airmon-ng tool, which is part of the aircrack-ng suite. To do this, run:
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You’ll get an output similar to the following:
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We’ll need to kill all those processes to prevent any issues. Simply issue kill commands for each process ID. Run airmon-ng check once again to be sure that all is well. We are now ready to scan for access points.
Scanning for access points
To run a wireless scan using a particular interface, run the following command:
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Your terminal screen will fill up with something like this:
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You’ll see a list of access points and devices associated with each access point. You’ll notice there are acronyms above each column. Here’s a list of the ones we care about and what they mean:
- BSSID - MAC Address of the access point
- PWR - Strength of the signal. The closer to 0, the better
- CH - Channel
- ESSID - Name of access point
- STATION - Device connected to access point (Laptop, smartphone, etc)
Now lets select an access point and run a scan on only that particular device. We’ll capture traffic and save it to a file. You’ll need to make note of the BSSID and channel of the access point. In my case, my router’s ESSID is “Lower The Rent”. We’ll scan it using the following command formula:
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In my case, the full command looks like this:
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Here’s the output:
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You’ll be able to see the access point and associated devices. This provides a much cleaner look instead of your terminal screen being full of information. We can see that there is a single device associated with the access point.
Now we can commence an attack.
Attacking an access point
We’ll be flooding the access point with deauthentication frames to keep devices from reconnecting to it. As they try to reconnect, we’ll be able to capture the 4-way handshake. This can also be used to simply perform DOS attacks on an access point. Keep in mind you won’t be able to capture the handshake if there are no devices associated to the access point. If there are no devices associated, there is nothing conducting the authentication process which you can capture.
While leaving the previous airodump-ng command running in a separate tab or window, open another tab to run the deauthentication command. The command is as follows:
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The BSSID we specify is that of the access point. It is possible to limit the amount of deauthentication frames to send, but in this case we are sending an infinite amount specified with -0 0.
The output for the aireplay-ng command will look like this:
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Your terminal screen will continue to fill with these messages. Keep the command running until you see a WPA handshake: XX:XX:XX:XX:XX:XX message on the upper right of the first window running the airodump-ng command. That window will look as follows (notice the message on the upper right):
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If you see the message, you have successfully captured the handshake. The last step left to do now is to crack this handshake and reveal the password in plaintext.
Cracking the password
Recall that we saved our airodump-ng scan to a file named SCAN_OUTPUT. You’ll see several files in the directory by the same name, but you’ll only need the one with a .cap extension. From here, there are two approaches to cracking the password. You can use a wordlist and see if one of the passwords in the wordlist is the actual password to the access point, or you can opt to use a program that generates passwords and attempts each one (brute forcing).
First, we’ll go over the approach using a wordlist. The command to begin cracking using a wordlist is as follows:
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In my case, I used a short wordlist of 4800 passwords to try and crack the handshake. I was not able to find the key, but this is what the output will look like:
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The tool will go through every password in the wordlist and try to crack the acess point’s password. Wordlists are convenient and can be fast, but if the password is not in the wordlist itself, we’ll need to try bruteforcing.
There are likely several tools out there that can generate password combinations, but I used crunch. The formula to feed passwords generated by crunch into aircrack-ng is as follows (notice we need to specify the ESSID this time):
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I already know the length of the passowrd to my own router. My full command looks like this:
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This will be very slow, as the program will attempt every 14-character letter and number combination possible.
In my case, my router has the default password of pinkcoconut165. With this knowledge, I can specify further. Instead of attempting a random mix of letters and numbers, I can test for a specific arrangement of letters/numbers. Obviously, this would not be known if we were attacking a completely unknown access point, but I want to demonstrate what a successful crack looks like. Using the -t option we can specify a pattern. Here’s the description from the man page:
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With this flag, we can modify our command as follows:
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This will still take long, however, due to the length of the password. Let’s cheat a little bit just to show the success screen. Here’s the new command where we will type in the letters of the password and only try to guess the remaining digits:
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Success! The password has been found:
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Additional Tips
Changing Your MAC Address
If you want to stay as anonymous as possible, you can change your MAC Address before attempting any of this. You can easily do this using a tool like macchanger. The following command will assign a randomized MAC address to the wlan0 interface:
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We can be more clever and use a MAC address from a known company. The first 3 bytes of a MAC address are known as the Organizationally Unique Identifier (OUI) and can identify the manufacturer. For example, some of Dell’s devices have the first 3 bytes as F8:DB:88. The last 3 bytes can be anything, as long as it is within the range of A-F and 0-9 (hexadecimal values).
We can specify a MAC address with the following command:
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On MacOS you can change the MAC address of an interface to one of your choosing with the following command:
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Using this knowledge of MAC Addresses, we can also determine the manufacturers of the access points we scan. We can look up the MAC addresses, figure out the manufacturer, and see if there are other vulnerabilities with specific device models. Maybe we’ll discover their formula for default passwords (which lots of people never change) to be, say, a combination of 5 letters and 5 numbers, which can help us crack the password. Any hint helps. Additionally, default ESSID names, such as “NETGEAR23-2G”, could mean that the user never changed the default password either ;).
Password Lists
Password lists are often used in password cracking to speed up the process. Instead of trying every possible combination of characters, we can try our luck using leaked passwords from one of these lists. A good place to find passwords lists and more is the SecLists GitHub repo. To start off, I suggest trying one of the “Common Credentials” lists.
Password lists can be used along with the crunch tool we used earlier. crunch has much more functionality that I did not dive into. I encourage you to read through the man pages and learn more about it. It’s versatile but still easy to pick up.
Conclusions
In this post I covered how to use aircrack-ng to scan for nearby access points, capture the 4-way handshake by sending spoofed deauthentication packets, and crack the hash using crunch. Once again, only try this on devices you own!
Scanning for wifi networks and acquiring handshakes is not too difficult. Anyone with some command line experience can achieve this. The hardest part will be cracking the password itself due to processing power required.
This is an example of why long passwords are important. It is not enough to add symbols to a short password. In fact, it is better to get into the habit of creating pass-phrases as opposed to pass-words. A combination of words with lowercase and capital letters in addition so symbols will be more secure than a single word with symbols. In other words, !ThisIsALongPassword123? is much harder to crack than Password123?
There are other tools that we could have used to crack the password, such as hashcat. If I’m not mistaken, hashcat can take advantage of a GPU which will allow you to crack passwords much faster. However, I wanted to focus on the tools that come with the aircrack-ng suite.
This concludes my wifi hacking notes, I hope you learned something!