fragattacks/research

Fragment and Forge: Breaking Wi-Fi Through Frame Aggregation and Fragmentation

Introduction

Our attacks affect all Wi-Fi networks. Note that the recent WPA3 specification only introduced a new authentication method, but its encryption ciphers (CCMP and GCMP) are identical to WPA2. Because of this, our attack is identical against WPA2 and WPA3 networks.

Older WPA networks by default use TKIP for encryption, and the applicability of our attacks against this cipher is discussed in the paper. Out of completeness, and to illustrate that Wi-Fi has been vulnerable since its creation, the paper also briefly discusses the applicability of our results against WEP.

Supported Network Cards

Only specific wireless network cards are supported. This is because some network cards may overwrite the sequence number of injected frames, may overwrite the fragment number, or reorder frames of different priority, and this interferes with our scripts (i.e. our script might incorrectly say a device is secure although it's not). We have confirmed that the following network cards work properly with our scripts:

Network Card	USB	5GHz	mixed mode	injection mode	hwsim mode (experimental)
Intel Wireless-AC 8265	No	Yes	patched driver	yes	as client
Intel Wireless-AC 3160	No	Yes	patched driver	yes	as client
Technoethical N150 HGA	Yes	No	patched driver/firmware	patched driver/firmware	patched driver/firmware
TP-Link TL-WN722N v1.x	Yes	No	patched driver/firmware	patched driver/firmware	patched driver/firmware
Alfa AWUS036NHA	Yes	No	patched driver/firmware	patched driver/firmware	patched driver/firmware
Alfa AWUS036ACM	Yes	Yes	patched driver????	yes	yes?
Alfa AWUS036ACH	Yes	Yes	no	patched driver	under development
Netgear WN111v2	Yes	No	patched driver	yes	yes

TODO: Verify 5 GHz and test it in practice.

TODO: No longer recommend Virtual Machine, but instead show whether it supports 5GHz?

TODO: AWUS036ACM iw set wlanX monitor active in injection mode (but in mixed mode that crashes)

TODO: Always recommend running our backported drivers to assure there are not unexpected regressions?

The three last colums signify:

1. Injection mode: whether the network card can be used as a second interface to inject frames in injection mode.

2. Mixed mode: whether the network card can be used in mixed mode.

3. Hwsim mode: whether the network card can be used in hwsim mode.

Yes indicates the card works out-of-the-box in the given mode. Patched driver/firmware means that the card is compatible when used in combination with patched drivers (and/or firmware). As client means the mode only works when the test script is acting as a client (i.e. you when are testing an AP). No means this mode is not supported.

We recommend the use of the Technoethical N150 HGA in either injection mode or mixed mode. This deivce requires the use of a patched driver and firmware, but since it's a USB dongle this can be configured inside a virtual machine. When using Virtual Box, we recommend to configure the VM to use a USB2.0 (OHCI + ECHI) controller, because we found the USB3.0 controller to be unreliable.

During our own tests, the AWUS036ACM dongle is supported by Linux, but at times was not correctly recognized during our experiments. It may be necessairy to use a recent Linux kernel, and manually executing sudo modprobe mt76x2u to load the driver. Unstable when used on a USB3.0 port. Otherwise works fine.

The AWUS036ACH was tested on Kali Linux after installing the driver using sudo apt install realtek-rtl88xxau-dkms. This device is generally not supported by default in most Linux distributions and requires manual installation of drivers. modprobe 88XXau rtw_monitor_retransmit=1

We tested the Intel AX200 as well and found that it is not compatible with our tool: its firmware crashes after sending a fragmented frame.

If you are unable to find one of the above network cards, you can search for alternative network cards that have a high chance of also working. When using a network card that is not explicitly support, we strongly recommend to first run the injection tests.

Prerequisites

Our scripts were tested on Kali Linux and Ubuntu 20.04. To install the required dependencies, execute:

# Kali Linux and Ubuntu
sudo apt-get update
sudo apt-get install libnl-3-dev libnl-genl-3-dev libnl-route-3-dev libssl-dev libdbus-1-dev git pkg-config build-essential macchanger net-tools python3-venv airmon-ng

Now clone this repository, build the tools, and configure a virtual python3 environment:

# **Self note: replace with real HTTP unauthenticated link on release**
git clone https://gitlab.com/aconf/wifi.git fragattack --recursive
cd fragattack
./build.sh
cd research
python3 -m venv venv
source venv/bin/activate
pip install wheel
pip install -r requirements.txt

The above instructions only have to be executed once.

Patched Drivers

Install patched drivers:

sudo apt-get install bison flex linux-headers-$(uname -r)
# **Self note: replace with real HTTP unauthenticated link on release instead of separate directory**
cd driver-backports-5.7-rc3-1
make defconfig-experiments
make -j 4
sudo make install

Install patched ath9k_htc firmware on Ubuntu:

cd research/ath9k-firmware/
sudo cp htc_9271.fw /lib/firmware/ath9k_htc/htc_9271-1.4.0.fw
sudo cp htc_7010.fw /lib/firmware/ath9k_htc/htc_7010-1.4.0.fw
# Now reboot the system

Note that the above directories depend on the specific Linux distribution you are running. If you Wi-Fi donle already is plugged in, unplug it. After installing the patched drivers and firmware you must reboot your system. The above instructions have to be executed again if your Linix kernel ever gets updated.

Before every usage

Every time you want to use the script, you first have to load the virtual python environment as root. This can be done using:

cd research
sudo su
source venv/bin/activate

You should now disable Wi-Fi in your network manager so it will not interfere with our scripts. Also make sure no other network services are causing outgoing traffic. You can assure this by using iptables rules by executing ./droptraffic.sh (you can revert this by rebooting). Optionally check using sudo airmon-ng check to see which other processing might interfere.

Our script can test both clients and APs:

• Testing APs: configure the AP you want to test by editing research/client.conf. This is a standard wpa_supplicant configuration file, see the [hostap documentation] on how to edit it.

• Testing clients: you must execute the script with the extra --ap parameter. This instructs the script into creating an AP with as name testnetwork and password abcdefgh. Connect to this network with the client you want to test. By default the client must request an IP using DHCP. To edit properties of the created AP, such as the channel it's created on, you can edit research/hostapd.conf.

Testing Modes

Injection mode

This mode requires two wireless network cards: one will act as an AP or the client, and the other one will be used to inject frames. Execute the script in this mode using:

./fragattack wlan0 --inject wlan1 [--ap] $COMMAND

Here interface wlan0 will act as a legitimate client or AP, and wlan1 will be used to inject frames. For wlan0, any card that supports normal client or AP mode on Linux can be used. For wlan1, a card must be used that supports injection mode according to Supported Network Cards.

In case the tests do not seem to be working, you can confirm that injection is properly working using:

./test-injection wlan1 wlan0

This will script will inject frames using interface wlan1, and uses wlan0 to check if frames are properly injected. Note that both interfaces need to support monitor mode for this script to work.

TODO: First test a normal ping. Frames may not arrive because the target is sleeping!

Mixed mode

This mode requires only one wireless network card. This disadvantage is that this mode requires a patched driver and/or firmware, and that only a small amount of network cards are supported. Execute the script in this mode using:

./fragattack wlan0 [--ap] $COMMAND

See Supported Network Cards for network cards that support this mode. For most network cards, this mode requires the installation of modified drivers and/or firmware. See Patched Drivers on how to install our patched drivers/firmware.

Hwsim mode

This mode is experimental and only for research purposes. See hwsim mode details for more information.

Testing for Vulnerabilities

Before testing for vulnerabilities we recommand to execute the first five commands in the table below. The first command performs a normal ping and can be used to confirm that the test setup works. The second performs a fragmented ping, and the third can be used to determine how time- sensitive attacks against the device would be.

The commands that test for vulnerabilities are grouped by their type along with a reference to the paper in which section the vulnerability is explained.

Command	Short description
ping I,E	Send a normal ping
ping I,E,E	Send a normal fragmented ping
ping I,E,E --delay 5	Send a normal fragmented ping with a 5 second delay between fragments
ping-frag-sep	Send a normal fragmented ping with fragments separated by another frame
A-MSDU attacks (Section 3)
ping I,E --amsdu	Send a normal ping encapsulated in a normal A-MSDU frame.
ping I,E,E --amsdu	Send a normal ping an a fragmented A-MSDU frame.
amsdu-inject	Send a valid A-MSDU frame whose start is also a valid LLC/SNAP header.
amsdu-inject linux	Same as above, but works against targets that incorrectly parse the frame.
Mixed key attacks (Section 4)
ping I,R,BE,AE	Inject two fragments encrypted under a different key.
ping I,R,BE,AE --pn-per-qos	Same as above, but also works if the target only accepts consecutive fragments.
Cache attacks (Section 5)
ping I,E,C,AE	Inject a fragment then reconnect (as client reassociate) and inject second fragment.
ping I,E,C,E	Same as above, but with a longer delay before sending the second fragment.
ping I,E,C,AE --full-reconnect	Inject a fragment, reconnect, then inject second fragment.
ping I,E,C,E --full-reconnect	Same as above, but with a longer delay before sending the second fragment.
Non-consecutive (Section 6.2)
ping I,E,E --inc-pn 2	Send a fragmented ping with non-consecutive packet numbers.
Mixed plain/enc (Section 6.3)
ping I,E,P	Send a fragmented ping: first fragment encrypted, second fragment in plaintext.
ping I,P,E	Send a fragmented ping: first fragment in plaintext, send fragment encrypted.
ping I,P	Send a plaintext ping.
ping I,P,P	Send a fragmented ping: both fragments are sent in plaintext.
linux-plain	Mixed plaintext/encrypted fragmentation attack specific to Linux.
EAPOL forwarding (Section 6.4)
eapol-inject 00:11:22:33:44:55	Test if the AP forwards EAPOL frames before being connected.
Broadcast fragments (Section 6.7)
ping I,D,P --bcast-ra	Send ping in a 2nd plaintext broadcasted fragment.
EAPOL A-MSDUs (Section 6.8)
eapol-amsdu BB	Send A-MSDU frame disguised as EAPOL frame. Use tcpdump to check if vulnerable.
eapol-amsdu I,CC	Same as above, except the frame is injected after obtaining an IP.
eapol-amsdu M,BB	Send a malformed A-MSDU disguised as EAPOL. Use tcpdump to check if vulnerable.
eapol-amsdu M,I,CC	Same as above, except the frame is injected after obtaining an IP.

Notable remarks:

• ping I,E,E --delay 5: this test is used to check the maximum accepted delay between two fragments. If the default test doesn't work, try with --delay 1.5 or lower. In case the maximum accepted delay is low, this may impact other tests. In particular, all fragments sent in other tests must be sent within the maximum delay, otherwise the test will trivially fail (and you might conclude a device isn't vulnerable to an attack even though it might be).

• Mixed key attacks: When running the mixed key test against an AP, the AP must be configured to regularly renew the PTK by executing a new 4-way handshake (e.g. every 30 seconds or minute). Against a low number of APs, the client can also request the AP to renew the PTK. This can be done by adding the --rekey-request parameter.

  Home routers with a MediaTek driver will perform the rekey handshake in plaintext. To test these devices, also add the --rekey-plaintext parameter.

  Certain clients install the key too early during a pairwise session rekey. To test these devices, add the --rekey-early-install parameter and retry the test.

Checklist

In case the script doesn't appear to be working, check the following:

1. Check that no other process is using the network card (e.g. kill your network manager).

2. Check that you are using modified drivers if needed for your wireless network card. If you updated your kernel, you will need to recompile and reinstall the drivers.

3. Check that you are using modified firmware if needed for your wireless network card.

4. Assure the device you are testing doesn't enter sleep mode (causing it to miss injected frames). Or use a compatible device in mixed mode?

5. Run the injection tests to make sure injection is working properly.

6. Check that you machine isn't generating background traffic that interferes with the tests. In particular, disable networking in your OS, manually kill your DHCP client/server, etc. See also Before every usage.

7. Confirm that you are connecting to the correct network. Double-check client.conf.

8. Make sure the AP being tested is using (AES-)CCMP as the encryption algorithm.

9. If your Wi-Fi dongle is unreliable, use it from a live CD or USB. A virtual machine can be unreliable.

10. Confirm using a second monitor interface that no other frames are sent in between fragments. For instance, we found that our Intel device sometimes sends Block Ack Response Action frames between fragments.

Extended Vulnerability Tests

Optionally you can also run more advanced tests. These have a lower chance of uncovering new vulnerabilities, but against more exotic implementations these might reveal flaws that the normal tests could not detect.

Command	Short description
A-MSDU attacks (Section 3)
ping I,E --fake-amsdu	If this test succeeds, the A-MSDU flag is ignored (Section 3.5).
Mixed key attacks (Section 4)
ping I,E,R,AE	In case the delay between fragments must be small.
ping I,E,R,AE --rekey-plaintext	If the device performs the rekey handshake in plaintext.
ping I,E,R,AE --rekey-req --rekey-plain	Same as above, and actively request a rekey as client.
ping I,E,R,AE --rekey-early-install	Install the new key before sending message 4 as an AP.
ping I,R,BE,AE --freebsd	Mixed key attack against FreeBSD.
ping I,R,BE,E	In case the new key is installed relatively late.
Mixed plain/enc (Section 6.3)
ping I,E,P,E	Ping with first frag. encrypted, second plaintext, third encrypted.
linux-plain 3	Same as linux-plain but decoy fragment is sent using QoS priority 3.
EAPOL forwarding (Section 6.4)
eapol-inject L,00:11:22:33:44:55	Try to make the AP send fragmented frames by EAPOL injection.
No fragmentation support (Section 6.6)
ping I,E,D	Send ping inside an encrypted first fragment (no 2nd fragment).
ping I,D,E	Send ping inside an encrypted second fragment (no 1st fragment).
Broadcast fragments (Section 6.7)
ping D,SP --bcast-ra	Ping in a 2nd plaintext broadcasted fragment before 4-way handshake.
ping D,BP --bcast-ra	Ping in a 2nd plaintext broadcasted fragment during 4-way handshake.
ping I,P --bcast-ra	Ping in a plaintext broadcast Wi-Fi frame after 4-way handshake.
macos CC	Experimental attack against macos.
macos BB	Same as above, but inject during 4-way handshake.
EAPOL A-MSDUs (Section 6.8)
eapol-amsdu [M,]BB --bcast-dst	Same as "eapol-amsdu [M,]BB" but ping is broadcasted.
eapol-amsdu [M,]I,CC --bcast-dst	Same as "eapol-amsdu [M,]I,CC" but ping is broadcasted.
eapol-amsdu SS	Same as "eapol-amsd BB" but inject frame before 4-way handshake.
eapol-amsdu AA	Same as "eapol-amsd BB" but inject frame right after 4-way handshake.

Advanced Usage

Network card injection test

The script test-injection.py can be used to test whether frames are properly injected when using injection mode:

./test-injection.py wlan0 wlan1

Here we test if network card wlan0 properly injects frames and we use network card wlan1 to monitor whether frames are properly injected.

TODO: In case tests are not working, try to first unplug USB dongles and reboot the device(s). If the tests still fail, try to use a different network card to monitor whether frames are injected properly.

TODO: Testing the TP-Link against the Intel 3160 was very unreliable: many frames were not received although they in fact were sent by the device.

Ack behaviour is best tested postauth so the client will not disconnected.

In case you do not have a second network card, you can execute a partial injection test using:

./test-injection.py wlan0

Unfortunately, the above test can only test if the kernel overwrites fields of injected frames, it cannot test whether the firmware or wireless chip itself overwrites fields.

To test whether a network card properly injects frames in mixed mode, you can execute the following two commands:

./fragattack wlan0 ping --inject-test wlan1
./fragattack wlan0 ping --inject-test wlan1 --ap

Here we test whether wlan0 properly injects frames by monitor the injected frames using the second network card wlan1. The first command tests if frames are properly injected when using mixed mode as a client, and the second when using mixed mode as a client. In order to start the test, the client must be able to connect to a network, and the AP waits until a client is connecting. In case you do not have a second network card, you can execute a partial mixed mode test using:

./fragattack wlan0 ping --inject-selftest
./fragattack wlan0 ping --inject-selftest --ap

Unfortunately, the above tests can only test if the kernel overwrites fields of injected frames, it cannot test whether the firmware or wireless chip itself overwrites fields.

Hwsim mode details

Warning: this is currently an experimental mode, only use it for research purposes.

This mode requires only one network card. The disadvantage is that this mode is the least reliable:

• Frames are handled slower, possibly causing the tested client/AP to timeout during authentication or association.

• When injeting frames, they may be retransmitted even though an acknowledgement was recieved. This will further slightly slowdown the handling of frames.

• Frames are not properly acknowledged depending on the wireless network card, which causes some tested clients or APs to disconnect during authentication or association.

Nevertheless, the advantage is that is mode requires only one wirelss network card and can, depending on the network card, be used without patches to the driver and/or firmware. Before using this mode, create two virtual network cards:

./hwsim.sh

This will output the two created virtual "hwsim" interfaces, for example wlan1 and wlan2. Then search for the channel of the AP you want to test, and put the real network card on this channel:

./scan.sh wlan0
iw wlan0 set type monitor
ifconfig wlan0 up
iw wlan0 set channel 11

You can now start the script as follows:

./fragattack wlan0 --hwsim wlan1,wlan2 [--ap] $COMMAND

After the script executed, you can directly run it again with a new command.

Static IP Configuration

In case the device you are testing doesn't support DHCP, you can manually specify the IP addresses that the script should use. For example:

./fragattack.py wlan0 ping --inject wlan1 --ip 192.168.100.10 --peerip 192.168.100.1

Here the testing script will use address 192.168.100.10, and it will inject a ping request to the peer IP address 192.168.100.1.

Alternative network cards

In case you cannot get access to one of the recommended wireless network cards, a second option is to get a network card that uses the same drivers on Linux. In particular, you can try:

• Network cards that use ath9k_htc

• Network cards that use iwlmvm

We recommend cards based on ath9khtc. Not all cards that use iwlmvm will be compatible. When using an alternative network card, we strongly recommend to first run the injection tests to confirm that the network card is compatible.

5 GHz support

In order to use our script on 5 GHz channels the network card being used must allow the injection of frames in the 5 GHz channel. Unfortunately, this is not always possible due to regulatory constraints. To see on which channels you can inject frames you can execute iw list and look under Frequencies for channels that are not marked as disabled, no IR, or radar detection. Note that these conditions may depend on your network card, the current configured country, and the AP you are connected to. For more information see, for example, the Arch Linux documentation.

Note that in mixed mode the Linux kernel may not allow the injection of frames even though it is allowed to send normal frames. This is because in ieee80211_monitor_start_xmit the kernel refuses to inject frames when cfg80211_reg_can_beacon returns false. As a result, Linux may refuse to inject frames even though this is actually allowed. Making cfg80211_reg_can_beacon return true under the correct conditions prevents this bug.

Notes on device support

TODO: Reference or include the DEVICES.md file

ath9k_htc

There is a known problem with the ath9k_htc driver, used by the Technoethical N150 HGA, TP-Link TL-WN722N v1.x, and Alfa AWUS036NHA, causing it not to work on kernel 5.7.3 and above. Downgrading to kernel 5.7.2 fixes this issue for now. More details are available at:

• Patch that might fix it: https://www.spinics.net/lists/linux-wireless/msg200825.html

• https://bugzilla.kernel.org/show_bug.cgi?id=208251

• https://bugzilla.redhat.com/show_bug.cgi?id=1848631

• https://lore.kernel.org/lkml/CAEJqkgjV8p6LtBV8YUGbNb0vYzKOQt4-AMAvYw5mzFr3eicyTg@mail.gmail.com/

AWUS036ACM

The reliability of our AWUS036ACM device, which uses the mt76x2u driver, varied depending on how it was used. We found that:

• On kernel 5.5.0 this device didn't work properly when connected to a USB3.0 port. In particular, it kept showing error: mt7602u_mcu_wait_resp failed with -108 when testing on Kali Linux. The device did work properly when connected to a USB2.0 port.

  Frame injection in the 2.4 GHz band was also working properly in the above setup. Frame injection was also working in the 5 GHz band (tested by running the test-injection,py script on channel 40 and capturing the frame using an Intel 3160).

  Strangely, this device refuses to inject frames when: (1) it's a data frame; (2) the destination MAC address is not all-zeros; and (3) the to-DS and from-DS are both not set. This was independent of the sender MAC address. Such frames are generally never sent anyway, so this has no practical impact, but it required us to tweak the test-injection.py script to always set the to-DS or from-DS flags.

  In mixed mode frames using the MAC address of the AP or client as sender MAC address were only being injected when injected after authentication. Before authenticating, these frames were dropped. In mixed client/monitor mode, the sequence counter of injected frames was being overwritten. In mixed AP/monitor mode, we were unable to inject frames towards the client when using the MAC address of the AP as the sender MAC address correctly (without the sequence counter being overwritten - we confirmed this with a fragmented ping against a client).

  TODO: test mixed mode with patched drivers

  Note: with an ath9k_htc we cannot inject frames with spoofed MAC addresses before and after authenticating in AP/monitor mode? It does inject frames (incorrectly) in client/monitor mode. This was likely because capturing with the Intel 3160 was very unreliable.

• On kernel 5.6.13 on Arch Linux, client mode didn't work properly when using an USB3.0 port. But AP mode did work properly on a USB3.0 port.

  In mixed mode, non-EAPOL data frames were not sent when injected before authentication. After authentication, these were transmitted. Is that patchable?

  Note: with an ath9k_htc we can inject frames with spoofed MAC addresses before and after authenticating in client/monitor mode. Same thing in AP/monitor mode. But capturing is unreliable.

TODOs

• Confirm each device can detect all vulnerabilities in the recommended modes.

• Test the attacks against PEAP-MSchap for eduroam tests (basic test was working).

• TODO: Is it important to disable encryption? I don't think it is. Otherwise we need sysfsutils as a dependency too.

• Create an example pcap and debug output of all tests.

• Release a known vulnerable linux image to test against? Essential to confirm the tests are working!

• sudo iw wlan0 set monitor otherbss. Does airmon-ng handle this better? Move to general section?

• Describe AP mode in hwsim mode?

• Support non-20MHz channels?