SecurityBSides Trainings
Course Description
Baseband exploitation is often considered the cream of the offensive security field. In the last decade, only a handful of such exploits were publicly released. As a result, many researchers view the ability to silently achieve code execution on a victim’s device by emulating a GSM or LTE base station as a difficult objective.
In reality, baseband exploitation is not as challenging! By following a simple list of steps, a baseband platform can be quickly opened up for research, debugging and exploitation. In this course, students will learn our systematic approach to baseband research - from setting up a fake base station using SDR and open-source BTS software, to achieving initial debugging abilities using our embedded hooking framework, and finally reverse engineering the relevant protocols, hunting for bugs and exploiting them.
By the end of this heavily hands-on course, students will become familiar with two extremely common baseband platforms, Shannon and MediaTek, gain the skills to debug these and other baseband platforms, and learn about previously discovered bugs in basebands, and how they have been exploited.
Prerequisite
- C and Python
- Good reverse engineering knowledge
- Familiarity with ARM assembly
- A working laptop
- 40 GB free Hard disk space
Instructor Bio - Pedro Ribeiro
Pedro Ribeiro is a vulnerability researcher and reverse engineer with over 15 years of experience. Pedro has found and exploited hundreds of vulnerabilities in software, hardware and firmware. He has over 160 CVE ID’s attributed to his name (most of which related to remote code execution vulnerabilities) and has authored over 60 Metasploit modules which have been released publicly. He also regularly competes in Pwn2Own as part of the Flashback Team, winning the coveted Master of Pwn in 2020. Besides his public vulnerability research activities, he is the founder and director of a penetration testing and reverse engineering consultancy based in London (Agile Information Security), and of an offensive security consultancy based in continental Europe (Vectorize). More information about Pedro’s publicly disclosed vulnerabilities can be found at github.com/pedrib/PoC. Flashback Team’s YouTube channel can be found at youtube.com/c/FlashbackTeam
Key Learning Objective
Agenda
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Room#1
Day 1: Introduction, initial analysis and debugging
Introduction to communication processors (CP):
- The evolution and challenges of communication systems
- Baseband processors: An architecture overview
- CP architectures: Broadcom, Qualcomm, MediaTek, Samsung
Code extraction and initial analysis:
- Challenges of baseband code extraction
- Getting the firmware
- Initial analysis: Parsing the firmware header
- Loading into IDA: Base addresses and program segmentation
Understanding baseband Real Time Operating Systems (RTOS):
- Data structures and IPC
- Memory permissions and mappings
- Mapping the attack surface
- Identifying functions and symbols in the code and writing a function mapping script
- Extracting debug strings and parsing them to name functions in the IDB
Debugging:
- Obtaining memory dumps
- Getting RWX permissions
- Building a debugger
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Room#1
Day 2: Cellular protocols and static analysis
Introduction to GSM, GPRS and UMTS:
- Guide to the relevant 3GPP protocols
- Working with the specs
- Determining the protocol attack surface
- Real time packet captures, analyzing a sample PCAP
Shannon: Static analysis and an architecture overview:
- Tasks, memory management and code structure
- Debugging functionality
- Samsung IPC: Talking to the Application Processor
- The Platform Abstraction Layer and the HAL
Understanding baseband Real Time Operating Systems (RTOS):
- MediaTek: A comparison with Shannon:
- Nucleus OS: implementation in MediaTek
- Debugging the MediaTek baseband
- Interaction with the AP
Setting up a rogue BTS:
- Getting started with YateBTS
- Making phone calls and sending SMS over your own network
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Room#1
Day 3: Finding bugs in shannon and mediatek
2G and 3G sub-protocols:
- Full reversing of a CC handler function in Shannon and in MediaTek
- Adapting YateBTS to run with GPRS and a primer on the protocol
Vulnerability research in LTE and 5G:
- The additional complexities of setting up an eNodeB
- Working with mutual authentication
- Enumerating pre-authentication attack surfaces
Finding Shannon bugs:
- Guiding the students towards finding a Shannon bug presented at Pwn2Own 2018
- Guiding the students towards finding a recent Shannon bug that was silently patched
- Enumerating related parsers
Finding MediaTek bugs:
- Guiding the students towards finding a GPRS bug in MediaTek (DoS)
- Analysing the bug using the adapted hooking framework
- Opening related attack surfaces in MediaTek
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Room#1
Day 4: Exploiting a Shannon n-day
Modifying YateBTS code to deliver the exploit payload
Exploit primitives:
- Restoring execution after a Shannon stack overflow – resuming the message parsing loop
- Exploiting heap overflows in Shannon OS
- Analysing the stack and heap for secondary exploitation primitives
- Challenges/exploit mitigations
Achieving code execution:
- Developing a proof of concept (PoC)
- Using ROP for a full exploit
- Loading the initial shellcode stub into global memory
- Building a custom bridgehead – receiving the main payload over the air
- Second stage: Modifying the system’s behaviour in order to capture traffic or escalate to the AP
Baseband emulation for vulnerability research
Escalating to the Application Processor (AP) and Android - an introduction
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