Man-in-the-Middle Attacks with HydraLinks for Automotive Penetration Testing

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1. Introduction

Modern automotive systems rely on Electronic Control Units (ECUs) communicating via Ethernet-based protocols (e.g., 100BASE-T1, 1000BASE-T1). As these networks expand in complexity, security researchers need a reliable method to intercept, analyze, and possibly manipulate traffic between two endpoints—be it two ECUs or an ECU and a diagnostic tool.

A Man-in-the-Middle (MitM) setup using two HydraLinks and a Linux bridge enables you to sit transparently between these devices, capturing traffic at Layer 2 without alerting the endpoints. Below is a straightforward guide to make this happen.

2. Requirements

1. Two HydraLinks Physical automotive Ethernet interfaces (100 Mbps or 1 Gbps capable).
2. Linux Workstation With root/sudo privileges, plus essential networking/bridging tools (bridge-utils, ip, ifconfig, tcpdump).
3. HydraLink Python Library Install: python -m pip install hydralink Driver/Repo: GitHub - dissecto-GmbH/hydralink
4. Optional Wireshark or tcpdump for traffic analysis. Scapy (or similar) for fuzzing, custom packet injection, and real-time manipulation.

3. HydraLink Modes and Speeds

HydraLinks support both slave and master modes and can run at 100 Mbps or 1 Gbps. Typically, one link must be in master mode, the other in slave mode, matching the real automotive environment (often the in-vehicle gateway is the master).

Common commands:

• Slave mode, 100 Mbps:

python -m hydralink        

• Master mode, 100 Mbps:

python -m hydralink -m        

• Slave mode, 1 Gbps:

python -m hydralink -g        

• Master mode, 1 Gbps:

python -m hydralink -m -g        

• GUI configuration (needs tkinter):

python -m hydralink --gui        

You can specify additional parameters (e.g., -d <MAC> or -p for promiscuous mode) to tailor the interface to your target environment.

4. Network Topology

[ Device A ] <---- Link A ----> [ Linux Bridge ] <---- Link B ----> [ Device B ]        

• Device A and Device B can be any two automotive network endpoints.
• Because the bridge operates at Layer 2, no changes are required on these devices. They believe they’re directly connected.

5. Creating the MitM Bridge in Linux

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5.1. Set Up HydraLink Interfaces

• Connect and configure Link A with the desired mode and MAC:

python -m hydralink -d 00:11:22:33:44:55        

• Configure Link B in a complementary mode (master vs. slave) and speed if necessary:

python -m hydralink -d 00:11:22:33:44:66 -m -g        

Your system should expose these interfaces (e.g., eth1, eth2) once they’re active.

5.2. Install and Check Bridge Utilities

sudo apt-get update
sudo apt-get install bridge-utils
brctl --help        

(Use your distro’s package manager if different.)

5.3. Create the Bridge Interface

sudo brctl addbr br0        

Check:

brctl show        

br0 should be listed, empty for now.

5.4. Add Interfaces to the Bridge

sudo brctl addif br0 eth1
sudo brctl addif br0 eth2        

Replace eth1/eth2 with whatever names HydraLink assigned.

5.5. Bring Everything Up

sudo ip link set br0 up
sudo ip link set eth1 up
sudo ip link set eth2 up        

If all is correct, bridging is operational. Devices A and B should pass traffic through br0.

5.6. Promiscuous Mode

Enabling promiscuous mode ensures you capture all frames (unicast, broadcast, etc.):

python -m hydralink -d 00:11:22:33:44:55 -p
python -m hydralink -d 00:11:22:33:44:66 -m -p        

Alternatively, set it manually using ifconfig <interface> promisc, but note that some packet-capture tools (e.g., tcpdump, Wireshark) will override this flag. Always verify after your tools are running.

6. Verifying the Setup

6.1. Connectivity Checks

• If Device A and B use IP, test with a basic ping to confirm bridging.
• Check link LEDs or logs for physical layer indications—no link, no traffic.

6.2. Packet Capture

Run tcpdump on br0:

sudo tcpdump -i br0        

If you see ARP requests, broadcast frames, or IP traffic, you’re set. For deeper analysis:

sudo tcpdump -i br0 -w capture.pcap        

Then open capture.pcap in Wireshark. If you’re working with automotive protocols like SOME/IP, DoIP, or UDS, you may need custom dissectors or manual inspection.

7. Analysis, Fuzzing, and Attack Scenarios

7.1. Protocol Analysis

• Check for Cleartext credentials or commands.
• Identify Legacy Protocols like Telnet/FTP, which indicate insecure practices.
• Security Access sequences in UDS 0x27 can be captured for further reverse engineering.

7.2. Fuzzing & Manipulation

• Scapy: craft malformed frames, inject them in real time.
• Real-Time Injection: intercept and modify ongoing traffic, flip bits in diagnostic requests, or insert spoofed frames.

7.3. Man-in-the-Middle Attacks

• Replay Attacks: record legitimate frames, replay them later to test for replay protections.
• Command Tampering: alter fields in real time (e.g., changing diagnostic session commands).
• ARP Spoofing: if using IP, standard network-level attacks still apply in automotive Ethernet.

8. Troubleshooting & Tips

1. Interface Naming: HydraLinks may not always appear as ethX. Check dmesg | grep eth or ip link show to find them.
2. Bridge IP Addressing: If you need your Linux host on the same network, assign an IP to br0, not to the HydraLink interfaces themselves: sudo ip addr add 192.168.1.10/24 dev br0
3. Reset the Bridge:

sudo ip link set br0 down
sudo brctl delbr br0 

Then re-add interfaces if the configuration gets messy.        

1. Speed and Duplex: Ensure you match the automotive network’s expected speed—100 Mbps or 1 Gbps.
2. Logs: Check system logs (journalctl -xe, dmesg) for error messages related to HydraLink drivers.

9. Automotive Pentesting Use Cases

1. Diagnostic Security: Intercept UDS or DoIP requests to see if they’re using encryption or if they accept unprotected flashing.
2. Firmware Updates: Some OEMs push updates over Ethernet. Inspect for insecure or unencrypted payloads.
3. Gateway Validation: Modern vehicles have a central gateway that enforces policy. Test it by injecting unexpected traffic.
4. Intrusion Detection: If a vehicle has an IDS/IPS, attempt fuzzing or malicious frames to see if it triggers defense mechanisms.
5. ECU Interaction: Some modules might broadcast sensitive data on the bus. Bridge sniffing captures these broadcasts.

10. Conclusion

A Man-in-the-Middle bridge with two HydraLinks provides a robust vantage point for sniffing, analyzing, and manipulating automotive network traffic. By inserting yourself at Layer 2, you gain full visibility of all frames, helping identify insecure protocols, unencrypted channels, and possible paths for exploitation.

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Further Reading & References

• HydraLink Driver/Repo: GitHub - dissecto-GmbH/hydralink
• Linux Bridge Utilities: Linux Foundation: bridge
• Wireshark: Wireshark.org
• tcpdump: tcpdump.org
• Scapy: GitHub - secdev/scapy

Happy hacking—and keep it responsible.