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Sniffle

Sniffle is a sniffer for Bluetooth 5 and 4.x (LE) using TI CC1352/CC26x2 hardware.

Sniffle has a number of useful features, including:

  • Support for BT5/4.2 extended length advertisement and data packets
  • Support for BT5 Channel Selection Algorithms #1 and #2
  • Support for all BT5 PHY modes (regular 1M, 2M, and coded modes)
  • Support for sniffing only advertisements and ignoring connections
  • Support for channel map, connection parameter, and PHY change operations
  • Support for advertisement filtering by MAC address and RSSI
  • Support for BT5 extended advertising (non-periodic)
  • Support for capturing advertisements from a target MAC on all three primary advertising channels using a single sniffer. This makes connection detection nearly 3x more reliable than most other sniffers that only sniff one advertising channel.
  • Easy to extend host-side software written in Python
  • PCAP export compatible with the Ubertooth
  • Wireshark compatible plugin

Prerequisites

If you don't want to go through the effort of setting up a build environment for the firmware, you can just flash prebuilt firmware binaries using UniFlash/DSLite. Prebuilt firmware binaries are attached to releases on the GitHub releases tab of this project. When using prebuilt firmware, be sure to use the Python code corresponding to the release tag rather than master to avoid compatibility issues with firmware that is behind the master branch.

Installing GCC

The arm-none-eabi-gcc provided through various Linux distributions' package manager often lacks some header files or requires some changes to linker configuration. For minimal hassle, I suggest using the ARM GCC linked above. You can just download and extract the prebuilt executables.

Installing the TI SDK

The TI SDK is provided as an executable binary that extracts a bunch of source code once you accept the license agreement. On Linux and Mac, the default installation directory is inside~/ti/. This works fine and my makefiles expect this path, so I suggest just going with the default here. The same applies for the TI SysConfig tool.

Once the SDK has been extracted, you will need to edit one makefile to match your build environment. Within ~/ti/simplelink_cc13xx_cc26xx_sdk_7_41_00_17 (or wherever the SDK was installed) there is a makefile named imports.mak. The only paths that need to be set here to build Sniffle are for GCC, XDC, cmake and SysConfig. We don't need the CCS compiler. See the diff below as an example, and adapt for wherever you installed things.

diff --git a/imports.mak b/imports.mak
index d3900b5b6..e7108c3df 100644
--- a/imports.mak
+++ b/imports.mak
@@ -18,14 +18,14 @@
 # will build using each non-empty *_ARMCOMPILER cgtool.
 #
 
-XDC_INSTALL_DIR        ?= /home/username/ti/xdctools_3_62_01_15_core
-SYSCONFIG_TOOL         ?= /home/username/ti/ccs1230/ccs/utils/sysconfig_1.18.1/sysconfig_cli.sh
+XDC_INSTALL_DIR        ?= $(HOME)/ti/xdctools_3_62_01_15_core
+SYSCONFIG_TOOL         ?= $(HOME)/ti/sysconfig_1.18.1/sysconfig_cli.sh
 
-CMAKE                  ?= /home/username/cmake-3.21.3/bin/cmake
+CMAKE                  ?= cmake
 PYTHON                 ?= python3
 
 TICLANG_ARMCOMPILER    ?= /home/username/ti/ccs1230/ccs/tools/compiler/ti-cgt-armllvm_3.2.0.LTS-0
-GCC_ARMCOMPILER        ?= /home/username/arm-none-eabi-gcc/9.2019.q4.major-0
+GCC_ARMCOMPILER        ?= $(HOME)/arm_tools/arm-gnu-toolchain-13.3.rel1-x86_64-arm-none-eabi
 IAR_ARMCOMPILER        ?= /home/username/iar9.40.2
 
 # Uncomment this to enable the TFM build

Obtaining DSLite

DSLite is TI's command line programming and debug server tool for XDS110 debuggers. The CC26xx and CC13xx Launchpad boards both include XDS110 debuggers. Unfortunately, TI does not provide a standalone command line DSLite download. The easiest way to obtain DSLite is to install UniFlash from TI. It's available for Linux, Mac, and Windows. The DSLite executable will be located at deskdb/content/TICloudAgent/linux/ccs_base/DebugServer/bin/DSLite relative to the UniFlash installation directory. On Linux, the default UniFlash installation directory is inside ~/ti/.

You should place the DSLite executable directory within your $PATH.

Firmware Building

Once the GCC, DSLite, and the SDK is installed and operational, building Sniffle should be straight forward. Just navigate to the fw directory and run make. If you didn't install the SDK to the default directory, you may need to edit SIMPLELINK_SDK_INSTALL_DIR in the makefile.

If building for or installing on a some variant of Launchpad other than CC26x2R, you must specify PLATFORM=xxx, either as an argument to make, or by defining it as an environment variable prior to invoking make. Supported values for PLATFORM can be found in the firmware makefile. Be sure to perform a make clean before building for a different platform.

Firmware Installation (TI Launchpad Board)

To install Sniffle on a (plugged in) CC26x2R Launchpad using DSLite, run make load within the fw directory. For any other Launchpad models, you must specify the PLATFORM argument to make as descirbed above. You can also flash the compiled sniffle.hex binary using the UniFlash GUI.

Firmware Installation (SONOFF USB Dongle)

To install Sniffle on a SONOFF CC2652P dongle (equipped with a CP2102 USB/UART bridge), you need to use a special firmware build that uses a 921600 baud rate (labelled 1M) instead of the default 2 megabit baud rate. You can use JelmerT/cc2538-bsl to flash the firmware using the built-in ROM bootloader with the following command:

python3 cc2538-bsl.py -p /dev/ttyUSB0 --bootloader-sonoff-usb -ewv sniffle_cc1352p1_cc2652p1_1M.hex

As of April 23, 2024, there are a couple bugs in cc2538-bsl for which pull requests 168 and 173 need to be merged to fix. In the interim, while waiting for those pull requests to be merged, you can use my fork at https://github.com/sultanqasim/cc2538-bsl.

WARNING: Do not flash the wrong build variant using the bootloader, or you risk bricking the device and locking yourself out of the bootloader. For Sonoff CC2652P devices, use the sniffle_cc1352p1_cc2652p1_1M.hex file (CC2652P1F_1M build variant). If you flash the wrong variant and lock yourself out of the bootloader, it may be possible to recover the device using JTAG/SWD.

Newer Sonoff dongles contain a CP2102N instead of the old CP2102. The CP2102N supports higher baud rates, including 2M and 3M baud. However, there is no easy and cross-platform way to distinguish between the CP2102 and CP2102N in software. Thus, the Sniffle host software expects the 1M (921600 baud) firmware on all devices with a CP2102/CP2102N USB/UART bridge. This slower baud rate should be fine for nearly all use cases, though in theory it may be possible to saturate the UART interface with the 2M PHY. If you really want to use the full 2M baud rate on your newer CP2102N equipped Sonoff (or other brand) dongle, you can flash the full baud rate firmware and modify sniffle_hw.py to not lower the baud rate for CP2102 devices.

Firmware Installation (Catsniffer V3)

Electronic Cats provides a Catnip Uploader tool for loading firmware. For detailed information, refer to the repository. Download the tool and follow these commands:

# Fetch the CatSniffer tools and their dependencies
[ec@sniffle]$ git clone https://github.com/ElectronicCats/CatSniffer-Tools.git
[ec@sniffle]$ cd CatSniffer-Tools/catnip_uploader
[ec@sniffle]$ pip install -r requirements.txt

# Download the available firmwares
[ec@sniffle]$ python3 catnip_uploader.py releases
[INFO] Fetching assets from https://api.github.com/repos/ElectronicCats/CatSniffer-Firmware/releases/latest
[INFO] Release: board-v3.x-v1.1.0
[INFO] Fetching assets from https://api.github.com/repos/nccgroup/Sniffle/releases/latest
[INFO] Release: v1.10.0
[INFO] Found local release: releases_board-v3.x-v1.1.0
[SUCCESS] Local release is up to date: board-v3.x-v1.1.0
[SUCCESS] Available releases:
0: sniffer_fw_CC1352P_7_v1.10.hex
1: airtag_scanner_CC1352P_7_v1.0.hex
2: nccgroup_v1.10.0_sniffle_cc1352p7_1M.hex
3: airtag_spoofer_CC1352P_7_v1.0.hex
4: sniffle_CC1352P_7_v1.7.hex

# Install the firmware
[ec@sniffle]$ python3 catnip_uploader.py load 2 COMPORT

You need to change the COMPORT to the appropriate path for your board. Using the command python3 catnip_uploader.py load 2 COMPORT, you will load the 2: nccgroup_v1.10.0_sniffle_cc1352p7_1M.hex firmware. To load the firmware Catsniffer V3 requires SerialPassthroughwithboot.

WARNING: Do not flash the wrong build variant using the bootloader, or you risk bricking the device and locking yourself out of the bootloader. If you use the catnip_uploader.py script to fetch and install the firmware, it will only present compatible firmware. However, if you choose to compile and install the firmware manually, be sure you use the correct build variant. For CatSniffer v3 devices, use the sniffle_cc1352p7_1M.hex file (CC1352P74_1M build variant). CatSniffer v1.x/v2.x devices use a different chip variant (CC1352P1) that needs a different firmware build (CC1352P1F3_1M variant, sniffle_cc1352p1_cc2652p1_1M.hex image). Sniffle has not been tested on CatSniffer v1.x/v2.x devices but they will probably work as long as you flash the appropriate build variant. If you flash the wrong variant and lock yourself out of the bootloader, it may be possible to recover the device using JTAG/SWD.

Sniffer Usage

[skhan@serpent python_cli]$ ./sniff_receiver.py --help
usage: sniff_receiver.py [-h] [-s SERPORT] [-c {37,38,39}] [-p] [-r RSSI] [-m MAC] [-i IRK]
                         [-S STRING] [-a] [-A] [-e] [-H] [-l] [-q] [-Q PRELOAD] [-n] [-C]
                         [-d] [-o OUTPUT]

Host-side receiver for Sniffle BLE5 sniffer

options:
  -h, --help            show this help message and exit
  -s SERPORT, --serport SERPORT
                        Sniffer serial port name
  -c {37,38,39}, --advchan {37,38,39}
                        Advertising channel to listen on
  -p, --pause           Pause sniffer after disconnect
  -r RSSI, --rssi RSSI  Filter packets by minimum RSSI
  -m MAC, --mac MAC     Filter packets by advertiser MAC
  -i IRK, --irk IRK     Filter packets by advertiser IRK
  -S STRING, --string STRING
                        Filter for advertisements containing the specified string
  -a, --advonly         Passive scanning, don't follow connections
  -A, --scan            Active scanning, don't follow connections
  -e, --extadv          Capture BT5 extended (auxiliary) advertising
  -H, --hop             Hop primary advertising channels in extended mode
  -l, --longrange       Use long range (coded) PHY for primary advertising
  -q, --quiet           Don't display empty packets
  -Q PRELOAD, --preload PRELOAD
                        Preload expected encrypted connection parameter changes
  -n, --nophychange     Ignore encrypted PHY mode changes
  -C, --crcerr          Capture packets with CRC errors
  -d, --decode          Decode advertising data
  -o OUTPUT, --output OUTPUT
                        PCAP output file name

The XDS110 debugger on the Launchpad boards creates two serial ports. On Linux, they are typically named ttyACM0 and ttyACM1. The first of the two created serial ports is used to communicate with Sniffle. By default, the Python CLI communicates using the first CDC-ACM device it sees matching the TI XDS110 USB VID:PID combo, or the first Sonoff dongle it sees. You may need to override this with the -s command line option if you are using a different USB serial adapter or have additional USB CDC-ACM devices connected.

For the -r (RSSI filter) option, a value of -40 tends to work well if the sniffer is very close to or nearly touching the transmitting device. The RSSI filter is very useful for ignoring irrelevant advertisements in a busy RF environment. The RSSI filter is only active when capturing advertisements, as you always want to capture data channel traffic for a connection being followed. You probably don't want to use an RSSI filter when MAC filtering is active, as you may lose advertisements from the MAC address of interest when the RSSI is too low.

To hop along with advertisements and have reliable connection sniffing, you need to set up a MAC filter with the -m option. You should specify the MAC address of the peripheral device, not the central device. To figure out which MAC address to sniff, you can run the sniffer with RSSI filtering while placing the sniffer near the target. This will show you advertisements from the target device including its MAC address. It should be noted that many BLE devices advertise with a randomized MAC address rather than their "real" fixed MAC written on a label.

Most new BLE devices use Resolvable Private Addresses (RPAs) rather than fixed static or public addresses. While you can set up a MAC filter to a particular RPA, devices periodically change their RPA. RPAs can can be resolved (associated with a particular device) if the Identity Resolving Key (IRK) is known. Sniffle supports automated RPA resolution when the IRK is provided. This avoids the need to keep updating the MAC filter whenever the RPA changes. You can specify an IRK for Sniffle with the -i option; the IRK should be provided in hexadecimal format, with the most significant byte (MSB) first. Specifying an IRK allows Sniffle to channel hop with an advertiser the same way it does with a MAC filter. The IRK based MAC filtering feature (-i) is mutually exclusive with the static MAC filtering feature (-m).

There is also a convenience feature to automatically identify the MAC address of the advertiser whose advertisement or scan response contains a specified string (series of bytes). This is useful for devices with RPAs where the IRK is unknown, but the advertisement contains a sufficiently unique static string suitable for identification. This feature uses the -S option, with the string specified using standard escape sequences. For example, to look for an advertiser whose advertisement contains the hex byte sequence DE AD BE EF, specify -S "\xDE\xAD\xBE\xEF". To look for an advertiser with the string "hello", simply specify -S "hello". When the string search feature is used, initially all MAC addresses will be accepted till an advertisement containing the search string is found. After that, a MAC filter will be set up with the corresponding advertiser's MAC address, and any RSSI filter would be automatically disabled.

To enable following auxiliary pointers in Bluetooth 5 extended advertising, enable the -e option. To improve performance and reliability in extended advertising capture, this option disables hopping on the primary advertising channels, even when a MAC filter is set up. If you are unsure whether a connection will be established via legacy or extended advertising, you can enable the -H flag in conjunction with -e to perform primary channel hopping with legacy advertisements, and scheduled listening to extended advertisement auxiliary packets. When combining -e and -H, the reliability of connection detection may be reduced compared to hopping on primary (legacy) or secondary (extended) advertising channels alone.

To sniff the long range PHY on primary advertising channels, specify the -l option. Note that no hopping between primary advertising channels is supported in long range mode, since all long range advertising uses the BT5 extended mechanism. Under the extended mechanism, auxiliary pointers on all three primary channels point to the same auxiliary packet, so hopping between primary channels is unnecessary.

To not print empty data packets on screen while following a connection, use the -q flag. This makes it easier to observe meaningful communications in real time, but may obscure when connection following is flaky or lost.

For encrypted connections, Sniffle supports detecting connection parameter updates even when the encryption key is unknown, and it attempts to measure the new parameters. However, if you know the new connection interval and Instant delta to expect in encrypted connection parameter updates, you can specify them with the --preload/-Q option to improve performance/reliability. The expected Interval:DeltaInstant pair should be provided as colon separated integers. Interval is an integer representing multiples of 1.25 ms (as defined in LL_CONNECTION_UPDATE_IND). DeltaInstant is the number of connection events between when the connection update packet is transmitted and when the new parameters are applied. DeltaInstant must be greater than or equal to 6, as per the Bluetooth specification's requirements for master devices. If multiple encrypted parameter updates are expected, you can provide multiple parameter pairs, separated by commas (eg. 6:7,39:8). If you have a device that issues encrypted PHY update PDUs that don't change the PHY, or puts out encrypted LE power control PDUs without any PHY changes, you can use the --nophychange/-n option.

To stop the sniffer, press Ctrl-C.

If for some reason the sniffer firmware locks up and refuses to capture any traffic even with filters disabled, you should reset the sniffer MCU. On Launchpad boards, the reset button is located beside the micro USB port.

Scanner Usage

usage: scanner.py [-h] [-s SERPORT] [-c {37,38,39}] [-r RSSI] [-l]

Scanner utility for Sniffle BLE5 sniffer

optional arguments:
  -h, --help            show this help message and exit
  -s SERPORT, --serport SERPORT
                        Sniffer serial port name
  -c {37,38,39}, --advchan {37,38,39}
                        Advertising channel to listen on
  -r RSSI, --rssi RSSI  Filter packets by minimum RSSI
  -l, --longrange       Use long range (coded) PHY for primary advertising
  -o OUTPUT, --output OUTPUT
                        PCAP output file name

The scanner command line arguments work the same as the sniffer. The purpose of the scanner utility is to gather a list of nearby devices advertising, and actively issue scan requests for observed devices, without having the deluge of fast scrolling data you get with the sniffer utility. The hardware/firmware will enter an active scanning mode where it will report received advertisements, issue scan requests for scannable ones, and report received scan responses. The scanner utility will record and report observed MAC addresses only once without spamming the display. Once you're done capturing advertisements, press Ctrl-C to stop scanning and report the results. The scanner will show the last advertisement and scan response from each target. Scan results will be sorted by RSSI in descending order.

Usage Examples

Sniff all advertisements on channel 38, ignore RSSI < -50, stay on advertising channel even when CONNECT_REQs are seen.

./sniff_receiver.py -c 38 -r -50 -a

Sniff advertisements from MAC 12:34:56:78:9A:BC, stay on advertising channel even when CONNECT_REQs are seen, save advertisements to data1.pcap.

./sniff_receiver.py -m 12:34:56:78:9A:BC -a -o data1.pcap

Sniff advertisements and connections for the first MAC address seen with RSSI >= -40. The RSSI filter will be disabled automatically once a MAC address has been locked onto. Save captured data to data2.pcap.

./sniff_receiver.py -m top -r -40 -o data2.pcap

Sniff advertisements and connections from the peripheral with big endian IRK 4E0BEA5355866BE38EF0AC2E3F0EBC22. Preload two expected encrypted connection parameter updates; the first with an Interval of 6, occuring at an instant 6 connection events after an encrypted LL_CONNECTION_UPDATE_IND is observed by the sniffer. The second expected encrypted connection update has an Interval of 39, and DeltaInstant of 6 too.

./sniff_receiver.py -i 4E0BEA5355866BE38EF0AC2E3F0EBC22 -Q 6:6,39:6

Sniff BT5 extended advertisements and connections from nearby (RSSI >= -55) devices.

./sniff_receiver.py -r -55 -e

Sniff legacy and extended advertisements and connections from the device with the specified MAC address. Save captured data to data3.pcap.

./sniff_receiver.py -eH -m 12:34:56:78:9A:BC -o data3.pcap

Sniff extended advertisements and connections using the long range primary PHY on channel 38.

./sniff_receiver.py -le -c 38

Actively scan on channel 39 for advertisements with RSSI greater than -50.

./scanner.py -c 39 -r -50

Obtaining the IRK

If you have a rooted Android phone, you can find IRKs (and LTKs) in the Bluedroid configuration file. On Android 8.1, this is located at /data/misc/bluedroid/bt_config.conf. The LE_LOCAL_KEY_IRK specifies the Android device's own IRK, and the first 16 bytes of LE_KEY_PID for every bonded device in the file indicate the bonded device's IRK. Be aware that keys stored in this file are little endian, so the byte order of keys in this file will need to be reversed. For example, the little endian IRK 22BC0E3F2EACF08EE36B865553EA0B4E needs to be changed to 4E0BEA5355866BE38EF0AC2E3F0EBC22 (big endian) when being passed to Sniffle with the -i option.

You can also find the IRK and LTK through HCI Snoop logs captured on Android or iOS without rooting the device:

Wireshark Plugin

Sniffle includes a Wireshark plugin that makes it possible to launch Sniffle automatically from the Wireshark GUI by selecting the 'Sniffle' capture interface.

To install the Sniffle plugin, first find the location of your Personal Extcap folder in the 'About Wireshark' dialog (Help > About Wireshark > Folders > Personal Extcap path). On POSIX (Linux and Mac OS) systems running recent versions of Wireshark (4.2.0+), this folder is located at ~/.local/lib/wireshark/extcap. Under Windows, it can be found at %USERPROFILE%\AppData\Roaming\Wireshark\extcap.

On POSIX systems, you can just symlink the Sniffle extcap plugin into the Wireshark personal extcap directory:

mkdir -p ~/.local/lib/wireshark/extcap
ln -s $(pwd)/python_cli/sniffle_extcap.py ~/.local/lib/wireshark/extcap

On Mac OS, Wireshark may try to use the Xcode Python rather than the Python in your PATH specified by your shell profile. Thus, the Sniffle plugin may fail to show up in extcap interfaces if PySerial is not installed for the Xcode Python. To fix this, you can edit the shebang line of sniffle_extcap.py to directly point to the Python with PySerial installed, for example the Homebrew Python at /opt/homebrew/bin/python3, rather than /usr/bin/env python3.

On Windows, you can copy the following files and directories from the python_cli directory into your Personal Extcap folder:

sniffle/
sniffle_extcap.py
sniffle_extcap.bat

On Windows, it may be necessary to edit sniffle_extcap.bat to specify the location of the python interpreter if the installation directory is not included in the PATH, e.g.:

@echo off
C:\my_python_install\python.exe "%~dp0sniffle_extcap.py" %*

Once the plugin has been installed, restart Wireshark or choose Capture > Refresh Interfaces to enable the Sniffle interface.

Transmit Functionality

While the original 2019 Sniffle firmware was purely a passive listener, later firmware versions added various features to actively transmit packets in various ways. Current Sniffle firmware supports acting as both a GAP central and peripheral device, including active scanning, legacy and extended advertising, initiating connections, and being connected in a master (central) or slave (peripheral) role. The scanner.py script performs active scanning. The initiator.py script initiates a connection to a peripheral and then acts as a connected master. The advertiser.py script performs legacy advertising and accepts connection requests from other devices, transitioning to a connected slave role.

The transmit functionality of Sniffle is a little different from a traditional HCI-based Bluetooth controller, because it gives you very low level control of the exact PDUs being sent at the link layer. This low-level control allows the host-side code to implement additional functionality, such as link layer fuzz testing or link layer relay attacks.

I have not yet taken the time to formally document the Sniffle firmware's API, though it is fairly self-explanatory when looking at its host-side implementation in sniffle_hw.py. Active scanning (that transmits scan requests) is activated by cmd_scan. Connection initiation is triggered by cmd_connect, though it's easiest to use the initiate_conn wrapper. Advertising (optionally connectable) is activated by cmd_advertise for legacy advertising, or cmd_advertise_ext for extended advertising.

XDS110 UART Latency

At least at the time of writing, the TI XDS110 debugger included in Launchpad boards has some undesirable behaviour in its USB to UART bridge, where at high baud rates, there can be severe latency, especially with frequent small writes as done by the Sniffle firmware. This issue has been present for years, and is still present as of April 2024 with the XDS110 firmware 3.0.0.28 bundled with UniFlash 8.6.0. The root cause is that in DMA based operation, the XDS110 firmware accumulates UART data in a buffer whose size is proportional to baud rate, and waits for this buffer to fill before transferring the data. There is logic to flush this buffer if no new data has arrived over the last 15 milliseconds, but this flushing logic is never triggered when Sniffle is frequently adding small packets from connection events every few milliseconds. As a result of this suboptimal behaviour, sniffed data can appear in delayed bursts on the host.

The XDS110 firmware also has an alternate mode for UART operation, where every UART receive triggers an interrupt that results in data immediately being passed to the host. This interrupt-based mode of operation has much lower latency. However, the firmware only uses it for baud rates below 230400. As a workaround to the high latency of DMA mode operation with frequent small data chunks, you can modify the firmware to use interrupt-based USB-UART bridging even at high baud rates (like 2M baud as used by Sniffle). In firmware 3.0.0.28 (included with Uniflash 8.6.0), you can hex edit the bytes at offset 0x0A14 from 61 3F to 00 1F. This will change the baud rate for switching to DMA-based UART operation from 230400 to 0x200000 (2097152).

Be aware that the offsets and byte modifications described above are only for firmware 3.0.0.28, and will be different for different firmware versions. Flashing invalid firmware onto your debugger may damage it, and we assume no responsibility for any damage that may occur.

The following commands can be used on Linux to modify the XDS110 firmware for low latency UART at high baud rates:

cd ~/ti/uniflash_8.6.0/deskdb/content/TICloudAgent/linux/ccs_base/common/uscif/xds110/
cp firmware_3.0.0.28.bin firmware_3.0.0.28_fastuart.bin
printf '\x00\x1f' | dd of=firmware_3.0.0.28_fastuart.bin bs=1 seek=$((0x0A14)) conv=notrunc
sha256sum firmware_3.0.0.28_fastuart.bin

Before flashing, verify that the SHA256 sum of the modified firmware is c226f2e9cb2b9f0bc111ca11f2903d58d4065293468623428c0e8eeb22086dcf. After verifying this, run the following commands to flash the modified XDS110 debugger firmware:

./xdsdfu -m
./xdsdfu -f firmware_3.0.0.28_fastuart.bin -r