CVE-2024-51500

Executive Summary

CVE-2024-51500 is a vulnerability in the Meshtastic firmware that allows a malicious actor to craft packets claiming to be from the special broadcast address (0xFFFFFFFF). The firmware does not validate the source address of incoming packets, leading to an amplification attack where a single malicious packet is rebroadcast by every node on the network. This can result in a Denial of Service (DoS) condition, consuming available bandwidth and degrading network performance for all users. The vulnerability has been addressed in firmware version 2.5.6, and all users are advised to upgrade. No workarounds are available.

CVSS Breakdown & Threat Level

• CVSS Score: 5.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
• Attack Vector (AV): Network (N) – The attack can be launched remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication is needed.
• User Interaction (UI): None (N) – No user action is required.
• Scope (S): Unchanged (U) – The impact is confined to the vulnerable component.
• Confidentiality (C): None (N) – No data is exposed.
• Integrity (I): None (N) – No data is altered.
• Availability (A): Low (L) – Network performance is degraded, but not completely denied.

Threat Level: Medium. The attack is easy to execute and can cause significant network disruption, but does not lead to data compromise.

Deep Dive & Mechanics

The Meshtastic firmware uses a broadcast address (0xFFFFFFFF) to send messages to all nodes on the network. The vulnerability lies in the lack of validation of the source address in incoming packets. A malicious actor can craft a packet with the source address set to 0xFFFFFFFF. When a node receives this packet, it treats it as a broadcast message and rebroadcasts it to all other nodes. Each receiving node then also rebroadcasts the packet, creating an amplification effect. This can quickly saturate the network with traffic, consuming all available bandwidth and causing a denial of service.

The core issue is in the packet processing logic, where the firmware does not check if the source address is the broadcast address. The fix involves adding a validation check to drop packets that claim to be from the broadcast address.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

void processPacket(Packet *pkt) {
    // No check on source address
    if (pkt->destination == BROADCAST_ADDR) {
        rebroadcast(pkt);
    }
}

Patched Code (Conceptual):

void processPacket(Packet *pkt) {
    // Check if source is broadcast address
    if (pkt->source == BROADCAST_ADDR) {
        dropPacket(pkt);
        return;
    }
    if (pkt->destination == BROADCAST_ADDR) {
        rebroadcast(pkt);
    }
}

The patched code adds a check to drop any packet where the source address equals the broadcast address, preventing the amplification attack.

Exploitation & Lab Setup

Red Team (Attack Simulation)

1. Setup: Deploy a Meshtastic network with at least two nodes running a vulnerable firmware version (< 2.5.6).
2. Craft Malicious Packet: Use a tool like meshtastic-python or a custom script to create a packet with source address 0xFFFFFFFF and any destination.
3. Send Packet: Transmit the crafted packet to one node in the network.
4. Observe: Monitor network traffic to see the packet being rebroadcast by all nodes, causing bandwidth saturation.

Example Python Script (Conceptual):

from meshtastic import mesh_pb2, tcp_interface
import time

interface = tcp_interface.TCPInterface(hostname="node_ip")

# Craft packet with broadcast source
packet = mesh_pb2.MeshPacket()
packet.from = 0xFFFFFFFF  # Broadcast source
packet.to = 0xFFFFFFFF    # Broadcast destination
packet.payload = b"malicious"

# Send packet
interface.send(packet)

Blue Team (Defense & Detection)

1. Monitor Network Traffic: Use Wireshark or tcpdump to capture LoRa packets and look for packets with source address 0xFFFFFFFF.
2. Firmware Upgrade: Immediately upgrade all nodes to firmware version 2.5.6 or later.
3. Network Segmentation: If possible, isolate Meshtastic networks from critical infrastructure.
4. Anomaly Detection: Implement rules to detect high volumes of broadcast traffic.

Indicators of Compromise (IOCs)

• Network Traffic: Packets with source address 0xFFFFFFFF (hex: FF FF FF FF).
• High Bandwidth Usage: Unusual increase in network traffic, especially broadcast messages.
• Node Behavior: Nodes rebroadcasting the same packet multiple times.

Detection Engineering

YARA Rule

rule Meshtastic_Broadcast_DoS {
    meta:
        description = "Detects packets with broadcast source address in Meshtastic firmware"
        author = "Valters IT"
        date = "2024-10-27"
        reference = "CVE-2024-51500"
    strings:
        $broadcast_src = { FF FF FF FF }
    condition:
        $broadcast_src
}

Sigma Rule

title: Meshtastic Broadcast Source Address Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects packets with source address 0xFFFFFFFF in Meshtastic network traffic
author: Valters IT
date: 2024/10/27
references:
    - https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-51500
logsource:
    category: network
    product: meshtastic
detection:
    selection:
        source_address: "0xFFFFFFFF"
    condition: selection
falsepositives:
    - None expected
level: high

Suricata Rule

alert udp any any -> any any (msg:"Meshtastic Broadcast Source Address Detected"; content:"|FF FF FF FF|"; offset:0; depth:4; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Upgrade Firmware: Update all Meshtastic nodes to firmware version 2.5.6 or later.
2. Network Monitoring: Continuously monitor for packets with source address 0xFFFFFFFF.
3. Access Control: Restrict physical access to Meshtastic nodes to prevent unauthorized packet injection.
4. Bandwidth Management: Implement rate limiting on broadcast messages to mitigate the impact of any future attacks.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert