slackin provides a self-service interface to join a slack team. I found it as a solution when I was setting up the mainesec slack team eliminating the need out unique links to every member that was joining. slackin creates a sign-up form where a user enters an email address and is automatically sent an invite to the slack team.
I have seen the script running in the Heroku cloud before but could not find any good instructions to install or run set it up other than a vague mention for a link to a button to automatically install it that did not exist.
This post covers the steps I went through to set-up a slackin instance in the Heroku cloud. To start off there are a couple of API keys that need to be created or gathered and used during the configuration.
Once the repo is forked to your account you will need to create a Heroku account (if you do not have one already). The free tier was sufficient for me to run the slackin.
Once you have logged into Heroku you will want to choose "New" and select "Create new app" in the upper right-hand corner. On the next screen, you will enter the App name, this will be used in the URL Heroku will generate for you.
Once you click the Create app button you will be sent to the Deploy tab. On this screen, select Github under the "Deployment method" section. (If you have not already connected your Github account to Heroku and you will need to and allow Heroku access to your repos.) Once connected, search for the forked slackin repo usually named "slackin" and click the Connect button.
Once connected you will need to deploy it to Heroku. There are a few options to deploy the app, for the first deployment I ran a Manual deploy by clicking the Deploy Branch button. This will take a while and will display any errors that occur.
Moving forward if you wish to have Heroku automatically deploy any changes you make in Github to the slackin app click the "Enable Automatic Deploys" button.
After the deploy is complete, select the Settings tab and add a few Config Vars. There are two settings that are required for slackin to operate. In these variables, we will enter the API keys you gathered earlier. The Google reCAPTCHA keys go into GOOGLE_CAPCHA_SECRET and GOOGLE_CAPCHA_SITEKEY. The Slack API keys go in SLACK_API_TOKEN and SLACK_SUBDOMAIN. the SLACK_SUBDOMAIN is the name of the Slack team that you are inviting users to.
Finally, to gather the URL that was assigned to the site you can scroll down on the Settings page to the Domains section and it is shown there.
You will now have a slackin instance setup for users to invite themselves to a slack team. For the mainesec team, I set up to domain redirection to the Heroku URL to make things a little simpler. If you encounter issues with slackin there is a lot of useful information in the Github issues for the main slackin repo.
Now that I have the lay of the land for the device (which that I outlined in my previous part of the series) the first thing I looked for is the debugging connections for the main GigaDevices processor. This processor looks to be the primary processor for the device and has the most valuable firmware. Since the board was well labeled I didn't need to use any tools like a JTAGulator or an Arduino board with the JTAGenum firmware to identify which test points are the debug interface. I was able to find the SWDIO, SWCLK, +3.3 and GND connections for the Serial Wire Debug (SWD) debug interface. This is the same interface that STM32 chips utilize and it provides similar functionality as a "standard" JTAG interface.
Serial Wire Debug (SWD) is a 2-pin (SWDIO/SWCLK) electrical alternative JTAG interface that has the same JTAG protocol on top. SWD uses an ARM CPU standard bi-directional wire protocol, defined in the ARM Debug Interface v5. This enables the debugger to become another AMBA bus master for access to system memory and peripheral or debug registers.
In the image below you can see the debug test points along with the with wires soldered to them to connect to my debugger. The proximity of these test points to the GD32F105 processor, it is a good assumption that they are for that chip.
As a bonus also pictured is my wire soldered around the switch on the upper left to bypass the intrusion detection function.
For this project, I soldered wires to most of the test points across the board. This board has a ton of test points that maybe be useful to monitor signals over the course of this project. To manage the wiring for all of the test points on this project I created a test jig to keep the setup organized. The next picture shows my test setup.
This jig was inspired by some tweets long ago by cybergibbons where he recommended doing something similar. Once all of the test wires were in place, I hooked up my ARM debugger of choice the Black Magic Probe (BMP) from 1BitSquared and the process to started to extract the firmware.
Initially, I tried to power the board using the BMP but I found that the BMP was not able to provide enough power to the board to support the minimum number of peripherals. The BMP can only supply 100mA of power. Some lights would come on but gdb would not detect any devices connected. I ended up adding the USB connection you see in the photo to provide more power to the board.
Now that everything is powered and connected I was able to use gdb to attach to the board and dump the firmware of the device.
Extracting the firmware: gdb
The first step is to attach my local arm gdb build to the Blackmagic Probe which acts as a remote gdb server. I always find the Useful GDB commands wiki page in the BMP wiki to be very useful in refreshing my memory. The syntax and terminal output I started with are:
╰─$ arm-none-eabi-gdb -ex "target extended-remote /dev/tty.usbmodemC2D9BBC31"
GNU gdb (GNU Tools for ARM Embedded Processors) 22.214.171.12460616-cvs
Copyright (C) 2015 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later http://gnu.org/licenses/gpl.html
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "--host=x86_64-apple-darwin10 --target=arm-none-eabi".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
Find the GDB manual and other documentation resources online at:
For help, type "help".
Type "apropos word" to search for commands related to "word".
/Users/locutus/.gdbinit:1: Error in sourced command file:
No symbol table is loaded. Use the "file" command.
Remote debugging using /dev/tty.usbmodemC2D9BBC31
Black Magic Probe (Firmware v1.6.1-1-g74af1f5) (Hardware Version 3)
Copyright (C) 2015 Black Sphere Technologies Ltd.
License GPLv3+: GNU GPL version 3 or later http://gnu.org/licenses/gpl.html
(gdb) monitor swdp_scan
Target voltage: 3.3V
No. Att Driver
1 STM32F1 high density
(gdb) attach 1
Attaching to Remote target
0x08007b46 in ?? ()
(gdb) dump binary memory firmware.bin 0x08000000 0x080FFFFF
Cannot access memory at address 0x8080000
When I ran into the error at the end of the terminal output I was a bit confused until I looked at this memory layout of the chip in the datasheet and saw that I was overrunning the size of the first flash memory bank.
╰─$ ls -l firmware.bin
-rw-r--r-- 1 locutus staff 524287 Nov 16 14:13 firmware.bin
I now have a copy of the firmware we can do some initial analysis of it.
First thing first like with any binary I start by running strings to get some hints on the contents of the binary and make sure it is a valid dump. I found a ton of strings showing this is a valid dump of the firmware, most notably the same markings on the board showing up in the firmware:
PCB:PG-103 VER2.3/FIRMWARE: 103-2G-J
and other strings indicate that they are using the Real-Time Operating system (RTOS) OS-III (link2) as the operating system. The Micrium site does not specifically list the Gigadevices chip in the supported just the general ARM Cortex-M3 cores as supported.
Seeing this let me know that reversing this firmware will be much more complex then I had hoped. The RTOS will add a lot of scheduling and random functions to look into. After this initial investigation, it is time to load the firmware into Radare. I used the following command when loading it up:
r2 -a arm -b 16 -m 0x0800c000 firmware.bin
This syntax sets the proper processor (-a) and CPU register size (-b) and starting memory location (-m). Once loaded I run an initial analysis job to see what Radare finds.
[x] Analyze all flags starting with sym. and entry0 (aa)
[x] Analyze function calls (aac)
[x] find and analyze function preludes (aap)
[x] Analyze len bytes of instructions for references (aar)
[x] Check for objc references
[x] Check for vtables
[x] Finding xrefs in noncode section with anal.in=io.maps
[x] Analyze value pointers (aav)
[x] Value from 0x0800c000 to 0x0808bfff (aav)
[x] 0x0800c000-0x0808bfff in 0x800c000-0x808bfff (aav)
[x] Emulate code to find computed references (aae)
[x] Type matching analysis for all functions (aaft)
[x] Use -AA or aaaa to perform additional experimental analysis.
[0x0800c000]> afl |wc -l
Radare found 844 functions without any hints or adjustments. In some of the work I have already done, there are even more than 844 functions. Now that I have a copy of the firmware, I've dived in and started analyzing the firmware which as of writing is still a work in progress. As I get further along I will cover some of the techniques I am using to take apart this firmware.
I was reminded of this tip during the CTF at a recent DC207 meetup. This config change is needed on machines with modern versions of OpenSSL that have disabled the older ciphers. The issue is that the old TLS, SSL and associated cipher suites have become insecure and support is subsequently dropped in OpenSSL.
For a workaround to this, you can edit the following lines at the bottom of /etc/ssl/openssl.cnf
The course costs at minimum $800 USD and includes 30 days of lab access and one OSCP exam attempt. There are packages that include longer lab access and you can extend your lab access if you find you need longer to prepare.
What ISN’T the OSCP
Current methods and techniques
It won’t make you a l33t hax0r, but you will learn fundamentals
How long did you study?
I started working on it on Sept 2018, then life and the holidays got in the way of dedicated study time. I kept slowly and intermittently practicing until April 2019 when I REALLY started to get serious about completing the OSCP. This started crunch time. I am lucky that my partner was on board with me locking my self away to focus on labbing. I took the exam on May 9th 2019.
How did you do to study?
I started by going through both the Offensive Security’s Penetration Testing with Kali Linux (PwK) workbook and then watching the associated videos. They are both fantastic resources providing a solid base of knowledge you need for the exam. I had the printed out the PwK workbook printed out and bound to save my eyes from staring at a screen. Through all my studies, I took a lot of notes. I used these notes when working on machines in the lab, exam, and other CTF style boxes I worked. Below are copies of the notes I created while studying.
Once I completed the workbook and videos, it was time to sit down and start to work on machines in the Lab. While working on the labs I began to branch out and gather and learn from various sources across the internet. As I worked through the lab and got closer to my date, I started to focus on my weak topics for me that were Windows Exploitation and Windows Privilege Escalation. I have added some of the main links and books I used to study, there are many more links in my notes.
Penetration Testing: A Hands-On Introduction to Hacking - Georgia Weidman
The Hacker Playbook: Practical Guide To Penetration Testing - Peter Kim
The Hacker Playbook 2: Practical Guide To Penetration Testing - Peter Kim
Hacking: The Art of Exploitation - Jon Erickson
OMG the Exam…
The OSCP exam is a practical test that is 24 hours of hacking in a mock environment attempting to break into various targets. You will then have another 24 hours to write a report based on your findings from the exam. To obtain your OSCP you must submit a report I'll talk more about the report later. The Exam is proctored, you will run software that will capture your screen and webcam, both of which will also be monitored by one or more proctors. There are limits to the tools you can during the Exam:
Spoofing (IP, ARP, DNS, NBNS, etc) Commercial tools or services (Metasploit Pro, Burp Pro, etc.) Automatic exploitation tools (e.g. db_autopwn, browser_autopwn, SQLmap, SQLninja etc.) Mass vulnerability scanners (e.g. Nessus, NeXpose, OpenVAS, Canvas, Core Impact, SAINT, etc.) Features in other tools that utilize either forbidden or restricted exam limitations You are limited to use Metasploit once during the lab
These limitations are an example of why it is important to fully read through the exam guide and reporting template to make sure you have all the proofs and meet the reporting requirements. These guides are found at the following links:
When planning for my Exam I created a high-level schedule to follow. This is an important and way for me to get organized. My exam started at 9:00 am allowing me to follow a similar routine to what I do normally.
Wake up … Breakfast
Connect to Proctor and follow preocess - 15 mins before start
Receive access details and connect to VPN - 15 mins
Read requirements and write down in notes - 30 - 45 mins
Initial Enumeration of targets - 1 hour
Probably still Hack…..
Exam Tips and Tactics
This is a list of various mostly non-technical tips I have for when taking the Exam. When reading through people's challenges on Reddit, Twitter and Blog posts I saw a lot of people ran into less than technical issues when taking their Exams.
I'll repeat this here make sure you read through the exam guide and reporting template to make sure you have all the proofs and meet the reporting requirements!
Attempt to limit distractions and find ways to go into flow
Manage your Time Management wisely
I used Pomodoro to help divide up my day. This method is ~25 minutes working, take a 5-minute break, repeat. I changed targets on each cycle if I was not making progress and was just grinding away on a machine. This method helped me getting stuck on one machine for extended periods of time.
Keep a timeline of the day
This will help you reference and screenshots or recordings you created later.
You are your own worst enemy: Avoid going down a rabbit hole
Breath…go for a walk…pet a cat…Have a snack...
Enumerate Enumerate Enumerate
If you are not finding your way into a system or the way to escalate privilege, enumerate more.
Screenshot, Screen record, track everything! This will take the stress off of creating the report the next day.
There are two topics when it comes to reporting there is the Lab report and the Exam report. Offensive Security provides a guide for reporting at the following URL: https://support.offensive-security.com/pwk-reporting/. This contains some templates and some recommendations on how to manage data.
One of the first questions people ask is if I did the Lab report. I decided not to do the Lab report, it only worth 5 points, and I did not find that the time to create the report was worth it for me. However, I did write a mock report to practice ahead of the Exam. The made sure that my first Exam reporting experience was not during the Exam when I would be exhausted.
When it comes to my Exam report, I started my report after I had finished my Exam but has not closed out with my proctor and start to create a very very very rough document with the screenshots and other content. I did this to make sure I had satisfied all of the requirements and it would let me go back and recreate or regather any Proofs I may have missed. After I thought I had everything and the adrenalin had started to wear off I went to sleep and got started the next day and finished the document throughout the next day.
The OSCP was a great experience and very challenging
There is a lot to learn
Make sure significant people in your life understand the time commitment
This is the first part of this adventure the next part will be exploring the firmware of the device. With that let's take a look at the hardware.
After the device showed up, I quickly got down to taking the device apart. In my haste, I didn't take many good photos of it intact. The front side of the board is straight forward; it contains the screen, button array for all user input, and a lot of useful test points. The front side is pictured below.
The most significant information found on the front side of the board is the notation PG-103, which is also found in the firmware (spoiler). After some searching, I found this device is also branded as the PGST PG-103. This kind of rebranding of hardware is not unusual for a lot of Chinese devices.
Now switching to the back of the board, which is the business side of the board with the main chips and modules providing the various communication methods. When opening that device I encountered the intrusion detection button. This button causes the device to go into an alarm mode and require a reset of the device to come back online. For my testing, I bypassed this button bridging both sides of it.
When inspecting the board, I found a few significant components and modules on the board. I was not surprised to see that most of the major communication parts are off the shelf modules. The components listed below are highlighted in the image above and the relevant data sheets where available are linked.
The main processor is a GigaDevice GD32 chip which is a series that is very similar to the of STMicroelectronics STM32 chips. The GD32F105 chip uses an ARM-based instruction set and has the same pinout as the STM32F105 component.
The high-level block diagram for the device is pretty straight forward. The GD32F105 chip is the primary processing and control of the external communication modules. This allows for a modular architecture all of the peripherals.
When exploring the board there are many test points on the board and tracing them out I was able to trace out most of the pins to where they connect on the controller.
SYN515R Pin 10 (DO) -> CPU PB9 (62)
Unknown -> CPU PA5
Unknown -> CPU PA6
Unknown -> CPU PA8
U7 SCL -> Unknown
U7 SDA -> Unknown
DAC_OUT -> CPU PA4 (20)
WIFI UART TX -> CPU PA2 (16)
WIFI UART RX -> CPU PA3 (17)
GSM UART TX -> CPU PA12 (45)
GSM UART RX -> CPU PA13 (46)
U1 (F117) Pin 6 -> CPU PB 8
After investigating the hardware I was able to extract the firmware and start the reversing process. I will cover what I have found in future posts. For now, if you are interested in more higher resolution photos of the board I have posted them on my Flickr account.
OpenSky is a proprietary trunking radio that is designed to carry both voice and data traffic. the protocol is marketed as to be secure and private. Opensky operates on the 700, 800, and 900 MHz bands.
OpenSky was originally developed by M/A-Com as part of the Monarch wireless voice and data system for FedEx in the 90s. Later M/A Com was purchased by Tyco Electronics who was then purchased by Harris RF Communications. Harris has now merged with L3 Technologies to become L3Harris. This protocol has gone on a wild ride of Mergers and Acquisitions for this protocol hasn't it? The original OpenSky protocol was upgrades in 2010 and named OpenSky2.
The integrated data capabilities in OpenSky allow for more features in one single base station than voice-only trunking systems. This integration has allowed for dispatchers to have location data for radios in the field and, the ability to send data to terminals in for example police car, and for users log into the handsets pulling down their profile with the various talk groups and other preferences.
OpenSky and OpenSky2 are TDMA based protocols they have been designed to operate using 25W micro repeaters. Opensky2 introduced support for the 900mhz band and a more narrow bandwidth. The table below lists them out.
Number of Slots
Raw bit rate (bps)
Channel Width (khz)
700 / 800
700 / 800 / 900
Signal Harbor describes there are 3 major components to the OpenSky signaling protocols:
FMP (Federal Express Mobile Protocol) - Providing Digital Voice
OCP (OpenSky Communication Protocol)
OTP (OpenSky Trunking Protocol)
These protocols are based off a modified CDPD (IS-732) similar to a an IS-54 (D-AMPS) network. I could not find a lot of exact details on lower level protocol operations other then Each radio assigned an IP address.
Digital voice is encoded using the Advanced Multi-Band Excitation (AMBE) speech encoding standard. This a proprietary standard that was developed by Digital Voice Systems, Inc. Interestingly this standard has been using in the Iridium Network and XM Satellite radio. There are more details on this standard here and here.
I found this protocol interesting because, like most technology, it's a product of it's time. In this case OpenSky comes from a time before the pervasive presence of 4G/LTE wireless. Today you can accomplish many of the same goals as a OpenSky system by utilizing the current carrier LTE networks.
Below is a list of resources I used when researching this protocol:
Back on May 18th, I attended the inaugural BsidesNH event. It was a fantastic one-day event. The day started pretty early for me driving down from Maine arriving at Southern NH University. I arrived to pick up the fantastic badge made out of an old 3.5" disk. After grabbing some coffee and a snack I settled into the auditorium and for a day of great talks. There were a few that stood out to me from the day that I will talk about.
The second talk of the day was Ghost in the Shell: When AppSec Goes Wrong by Tony Martin. Tony first talked about covered some basics of web application security. He framed these issues around the research he has done into various NAS devices and vulnerabilities he has discovered. Including the ability to create shadow users that have administrative access to devices but are not visible through the administrative interfaces of the device.
After lunch was Chinese and Russian Hacking Communities presented by Winnona DeSombre and Dan Byrnes, Intelligence Analyst from Recorded Future. They covered operations and cultures of Chinese and Russian underground groups. This was a very entertaining presentation and a summary of the information contained in the report: Thieves and Geeks: Russian and Chinese Hacking Communities.
The second to last talk of the day was Hunting for Lateral Movement: Offense, Defense, and Corgis presented by Ryan Nolette. He covered the ways attackers move around and infiltrate further into a network...Corgies. A great quote that stuck with me from his talk was: “If you teach an analyst how to think they will punch above their weight.” I feel this quote not only applies to security analysts but all levels of IT professionals.
BsidesNH was a well run and enjoyable event and a great addition to the Security events in New England. Thanks to all of the organizers and sponsors. I look forward to attending next year!