CaptureSetup/USB

USB capture setup

This page is about capturing raw USB traffic, e.g. the packets a USB mouse will generate on the Universal Serial Bus.

Table of contents

USB attached network interfaces

A special case are network interfaces connected to a host computer through an USB cable. The operating system "converts" the raw USB packets into the network traffic (e.g. Ethernet packets) and provides a network interface that looks like an ordinary network interface. So you can capture from:

The USB bus will add additional overhead, so the raw USB traffic will have higher volume than the network traffic, even if the only active USB devices on the system are network adapters. (If there are other active USB devices, the raw USB traffic will include traffic to and from those devices, so it will obviously have higher volume than Ethernet traffic.)

Software only URB capture

Software USB capture captures URBs (USB Request Blocks) rather than raw USB packets. URBs are referred to in USB 2.0 Specification Chapter 10 as IRPs that are submitted to USBDI. URBs carry transfers as seen by host USB stack rather than individual transactions. The individual packets as described in USB 2.0 Specification Chapter 8 are not possible to capture with software sniffers.

Linux

Capturing USB traffic on Linux is possible since Wireshark 1.2.0, libpcap 1.0.0, and Linux 2.6.11, using the Linux usbmon interface.

First, check if you belong to the wireshark group with:

groups $USER

To add yourself to the wireshark group, run the below command, then logout and login.

sudo adduser $USER wireshark

Then ensure that non-superusers are allowed to capture packets in wireshark. Select <Yes> in the below prompt:

sudo dpkg-reconfigure wireshark-common

The next two commands may need to be re-run after every reboot:

To dump USB traffic on Linux, you need the usbmon kernel module. If it is not loaded yet, run this command as root:

modprobe usbmon

To give regular users privileges, make the usbmonX device(s) readable:

sudo setfacl -m u:$USER:r /dev/usbmon*

On some Linux distributions (Arch Linux, Debian, Ubuntu, possibly others), the above command may not be necessary if you already belong to the wireshark group. See CaptureSetup/CapturePrivileges: Most UNIXes.

With Linux kernels prior to 2.6.23, you will also need to run this command as root:

mount -t debugfs none /sys/kernel/debug

and, with those kernels, the usbmon mechanism's protocol limits the total amount of data captured for each raw USB block to about 30 bytes. With a 2.6.23 or later kernel, and libpcap 1.1.0 and later, that size limitation is removed. Use uname -r to check your kernel version.

In libpcap 1.1.0 and later, the devices on which you can capture are named usbmonX, where X is the USB bus number. On Linux 2.6.22 and later, the special "usbmon0" interface receives a combined stream of events from all USB buses. In libpcap 1.0.x, the devices were named usbX.

Simple MITM hardware with Linux

If the USB host is a black-box device such as a game console and you cannot capture USB traffic on the host's operating system, here are two DIY-projects that help you build a simple MITM device to intercept and relay USB messages on the USB cable.

macOS

Capturing USB traffic on macOS is possible since Wireshark 2.4.0, libpcap 1.9.0, and macOS High Sierra, using the XHC20 interface.

In order to capture on that interface, you will first have to run the command

ifconfig XHC20 up

as root, for example by running

sudo ifconfig XHC20 up

In macOS Catalina and later releases, you apparently have to disable System Integrity Protection to capture USB traffic.

Windows

You can capture raw USB traffic on Windows with USBPcap. The Tools page lists some other options for Windows USB capture.

A word of warning about USBPcap

There have been problems with using USBPcap in the past, and while these problems should be resolved now, you may wish to familiarize yourself with these earlier problems, in the event you are still affected by it.

You can also capture and debug USB traffic on a virtual Windows machine under VirtualBox. In some ways this is more convenient than working with a separate Windows box.

In this example, an embedded Linux device running g_ether (RNDIS ethernet gadget) connects to Windows. e.g. an NSLU2 with a USB slave modification http://www.nslu2-linux.org/wiki/HowTo/AddDeviceSideUSBPort but it should work for almost any USB device.

With this method, Linux recognises the USB device (i.e. >lsusb will still show them), but VirtualBox hooks it into Windows but Wireshark on linux still gets to snoop on all the packets.

Steps:

1. Install a VirtualBox Windows guest on your Linux host. Start up the virtual Windows session.

2. Plug-in the embedded slave device via a USB cable, which itself should be either a device Windows already knows about (or in this case it was running a valid g_ether gadget stack and needed a .inf file)

3. Run >lsusb and take a note of which bus the device connects.

4. On linux side,run >ifconfig usb0 down - this prevents both the linux system and the windows system from fighting over the device

5. On the Windows virtual machine, on VirtualBox menus click the checkbox

6. Now Windows should recognise the device and proceed with the "plug-and-pray" session for driver initialisation.

I worked from the instructions on http://docwiki.gumstix.org/index.php/Windows_XP_usbnet to install the driver.

7. In this example, I had to set up the networking options for IP address, Gateway etc on Windows to match the IP network on the gadget but for other USB device types there will be no extra setup. In any case this is just normal Windows behavior.

8. On Linux, startup Wireshark and using the Bus number given earlier from >lsusb command to sniff for packets.

Hints for developing something like a Windows native "USBPcap": a kernel mode filter device driver has to be written. An older Driver Development Kit (DDK) is available which at least can compile kernel mode binaries. The most important functions to install the filter driver are CreateService() and SetupDiSetDeviceRegistryProperty() function with SPDRP_LOWERFILTERS parameter.

Hardware USB capture

Capturing raw packets as seen on the bus is possible with hardware USB sniffers. The target device is connected through the hardware sniffer in man-in-the-middle style:

Besides the two cables there is also a third cable from sniffer host USB B (or USB C) port to the capture host. It is recommended that capture host is separate from target host.

Currently there is no USB 3.x capture hardware available with Wireshark support.

OpenVizsla

OpenVizsla contains 32 MiB onboard SDRAM that is useful when capturing high-speed bus with significant saturation. Use ovextcap to make OpenVizsla interface available in Wireshark interfaces list.

OpenVizsla is Open Hardware project and can be assembled manually. Last known place where preassembled units were sold is sysmocom.

Low-cost USB Sniffer

Low-cost USB Sniffer (LS/FS/HS) with Wireshark interface is USB 2.0 bus sniffer without onboard RAM. Use usb sniffer extcap to make USB Sniffer interface available in Wireshark interfaces list.

Schematics are available in KiCad format and the hardware can be assembled manually.

Discussion

Why was the note about inaccurate time stamps removed?!? - UlfLamping

The timestamps should be ok now since libpcap works around the issue by explicitly calling gettimeofday()- ronnie

Well, the inaccuracies I had in mind was about the "delta" involved between the data is received from the USB device and actually timestamped from the kernel. This delta will be substantially lower for e.g. PCI based nic's than for USB ones - and should be mentioned. Or am I just wrong on this topic and this can be ignored - which should be mentioned then too? - UlfLamping

There's "capturing on USB-attached networking interfaces" and there's "capturing USB traffic"; this page is for the latter, but it sounds as if the time stamp delta is an issue for the former. - Guy Harris

See Also

Imported from https://wiki.wireshark.org/CaptureSetup/USB on 2020-08-11 23:12:03 UTC