Advanced Wi-Fi Attacks Using Commodity Hardware

We provide tools to perform low-layer attacks such as reactive and constant jamming using commodity devices. Reactive jamming allows you to block specific Wi-Fi packets. For example, all beacons and probe responses of a specific Access Point (AP) can be jammed. It has been tested with the following devices:

• TP-Link WN722N
• AWUS036NHA
• WNDA3200

This work was the result of the paper Advanced Wi-Fi Attacks Using Commodity Hardware presented at ACSAC 2014. If you use these tools in your research, please reference this paper. Most code is open source, and contributions are welcome. The code of the constant jammer can be requested but is not available publicly. Don't worry, we won't bite.

Quick start

You can download a VMWare image that has the drivers, firmware, and user-land tools preinstalled. Just boot it, plug-in the USB dongle, and start experimenting! The password of the account modwifi is modwifi. Once booted, you can execute (the public) attacks below.

Basic Usage

This section describes the attacks that can be executed. We assumed you already downloaded the VMWare image or manually installed the drivers and firmware (see the section "Installation" to install drivers on your existing machine).

Before doing any attacks it is recommended to disable WiFi. In particular I mean disabling WiFi in your network manager. Most graphical network managers have an option somewhere named "Enable Wi-Fi". Make sure it's not selected. If you can't find it, perhaps you can disable in the terminal with sudo nmcli nm wifi off. Once you have disabled WiFi your OS won't interfere with our attacks.

If RF-kill is enabled we'll have to turn it off. Some distributions set RF-kill on after disabling WiFi. But we still want to actually use our WiFi devices. So execute:

sudo apt-get install rfkill
sudo rfkill unblock wifi

Reactive Jamming

Our current implementation of our reactive jammer allows you to block an Access Point. More precisely, all beacons and probe responses will be jammed. Execute it using:

modwifi@ubuntu:~/modwifi/tools$ sudo rfkill unblock wifi
modwifi@ubuntu:~/modwifi/tools$ sudo iw wlan0 set type monitor
modwifi@ubuntu:~/modwifi/tools$ sudo ifconfig wlan0 up
modwifi@ubuntu:~/modwifi/tools$ sudo ./reactivejam -i wlan0 -s "Home Network"

The first three commands need to be executed only once after plugging in your dongle. You can stop the reactive jammer using CTRL+C. It may take a few seconds before it actually stops. By modifying the firmware you can reactive jam any kind of packets you like. For example, you could jam all packets of a specific client. Note that only medium to large packets can be reliably jammed (see our paper).

You can verify that this works by monitoring the channel with a second device. Make sure that this device also reports corrupted frames using:

sudo iw wlan1 set monitor fcsfail

This will instruct the driver to also pass corrupted frames to the userland (when in monitor mode). Be warned though, not all drivers properly support this flag. Some will always show corrupted frames. Others will never show corrupted frames. Our drivers and firmware handle this flag correctly!

Disabling Carrier Sense

Want to disable carrier sense in order to perform an experiment? Then execute this:

modwifi@ubuntu:~$ sudo su
root@ubuntu:~$ mount -t debugfs none /sys/kernel/debug
root@ubuntu:~$ cd /sys/kernel/debug/ieee80211/phy*/ath9k_htc/registers/
root@ubuntu:~$ echo 1 > force_channel_idle
root@ubuntu:~$ echo 1 > ignore_virt_cs

Writing 1 to force_channel_idle disables physical carrier sense (channel is busy). Writing 1 to ignore_virt_cs disables virtual carrier sense (RTS/CTS). Random backoff parameters can also be changed.

Constant Jamming

If you have the firmware capable of doing constant jamming, you can execute:

modwifi@ubuntu:~/modwifi/tools$ sudo iw wlan0 set type monitor
modwifi@ubuntu:~/modwifi/tools$ sudo ifconfig wlan0 up
modwifi@ubuntu:~/modwifi/tools$ sudo ./constantjam wlan0 6

This performs constant jamming on channel 6. Because channels overlap, nearby channels will also be jammed. Remember that the constant jamming implementation is not public, but can be requested personally.

Unfair Channel Usage

The specific scripts we used to easily configure a device to act unfairly are not public. The reason behind this is that it's hard to defend against these kind of attacks. However, some parameters can still be accessed as debugfs entries in /sys/kernel/debug/ieee80211/phy*/ath9k_htc/registers/.

Forcing Corrupt Packets

You can force the wireless chip to calculate a wrong CRC (FCS) using:

modwifi@ubuntu:~$ sudo su
root@ubuntu:~$ mount -t debugfs none /sys/kernel/debug
root@ubuntu:~$ cd /sys/kernel/debug/ieee80211/phy*/ath9k_htc/registers/
root@ubuntu:~$ echo 1 > diag_corrupt_fcs

TKIP Broadcast Attack

This is an advanced attack and not for the fainthearted. It clones an existing Access Point on a different channel. This allows us to reliably manipulate encrypted traffic. We used this to break TKIP. See our paper for details. An example on how we used it to verify that our awesome-sauce attacks work:

modwifi@ubuntu:~/modwifi/tools$ sudo ./channelmitm -a wlan4 -c wlan5 -j wlan3 -s testnetwork -d mitm.pcap --dual

Installation

You can also install the latest drivers and firmware on your own machine. The quickest method is to grab one of our release packages. Only your wireless driver for the devices mentioned above will be replaced, everything else stays the same. Normal usage of WiFi still works perfectly when these drivers are installed (I use these drivers myself :).

The installation instructions are:

mkdir modwifi && cd modwifi
wget https://github.com/vanhoefm/modwifi/raw/master/releases/modwifi-15012015.tar.gz
tar -xf modwifi-15012015.tar.gz

cd drivers && make defconfig-ath9k-debug
make
sudo make install
cd ..

sudo cp target_firmware/* /lib/firmware/
sudo apt-get install g++ libnl-dev libssl-dev
cd tools && make all

Reboot so our new drivers will be used. After that you should be good to go. That is, plug in your dongle, and execute the compiled tools.

If you want to compile the firmware as well, clone the ath9k-htc repository, and follow the instructions there. If you want to modify the driver, you can use the downloaded code in drivers.tar.xz. I recommend putting that code in our own repository to keep track of changes. But even better would be to apply patches to the latest Linux kernel, and then either compiling the kernel or using backports to create a release similar to mine. Still, the truly best option would be to contribute patches to this project (git pull request or just mail your patches)!

Source Code

The work is divided other several git repositories:

1. Linux: Forked Linux kernel to make driver modifications.
2. Backports: Fork of the backports projects so we can backport our drivers to older kernels.
3. Ath9k-htc: Forked firmware code to implement the core of our attacks.
4. Tools: New repository for our user-land tools.

You can download all repositories at once using the following commands:

mkdir modwifi && cd modwifi
bash <(curl -s https://raw.githubusercontent.com/vanhoefm/modwifi/master/init.sh)

Apart from the tools repositories, all work and modifications are performed on the research branch. When a new Linux kernel (or firmware) is released, we can easily merge with it. As a result our code is relatively easy to keep up-to-date.

For those who also want to start hacking away at the driver and firmware, I recommend first going reviewing our patches. This allows you to focus on a subset of code for each patch. That way it's easier to learn step by step. Maybe you will even find bugs or can make improvements (let us know). Also, in the ath9k-htc repository, there is a directory called docs. While still terse to read, these documents should be an excellent guide while reading and understanding the code.

If you have any questions, don't hesitate to send us a mail.