CVE-2024-50697

Executive Summary

CVE-2024-50697 is a critical stack-based buffer overflow vulnerability in SunGrow WiNet-SV200 devices, specifically in firmware versions up to and including WiNet-SV200.001.00.P027. The flaw resides in the MQTT message decryption routine, where the code parsing specific TLV (Type-Length-Value) fields lacks sufficient bounds checking. This allows an attacker to overflow a stack buffer, potentially leading to remote code execution (RCE) or denial of service (DoS). The vulnerability is currently unpatched, and no public exploit code or proof-of-concept is available. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains high due to the potential for full device compromise.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in an IoT device (SunGrow WiNet-SV200). No supply chain package security implications are present.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, but this is likely a placeholder. Based on the vulnerability type (stack-based buffer overflow in a network service), a realistic CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) – MQTT is a network protocol.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed to send MQTT messages.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerability affects only the device.
• Confidentiality (C): High (H) – Potential for full memory read.
• Integrity (I): High (H) – Potential for arbitrary code execution.
• Availability (A): High (H) – Potential for crash or DoS.

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

Threat Level: Critical. The vulnerability is remotely exploitable without authentication, and the device is often deployed in critical infrastructure (solar energy management).

Deep Dive & Mechanics

The vulnerability exists in the MQTT message decryption logic of the SunGrow WiNet-SV200 firmware. MQTT messages are used for device-to-cloud communication. The device decrypts incoming MQTT payloads and parses TLV fields. The TLV parser does not validate the length field against the available stack buffer size. By crafting a malicious MQTT message with an oversized TLV length value, an attacker can trigger a stack-based buffer overflow.

Technical Flow:

1. The device listens for MQTT messages on a specific topic (likely related to device configuration or commands).
2. Upon receiving a message, the device decrypts the payload using a hardcoded or weak key (common in IoT).
3. The decrypted payload is parsed for TLV fields. The parser reads the Type (1 byte), Length (2 bytes), and Value (Length bytes).
4. The Value is copied into a fixed-size stack buffer without checking if Length exceeds the buffer size.
5. An attacker sends a crafted MQTT message where the TLV Length field is set to a value larger than the stack buffer (e.g., 0xFFFF).
6. The memcpy or similar function overflows the stack, overwriting the return address and other critical data.
7. This can lead to arbitrary code execution in the context of the MQTT service (often running as root).

Root Cause: Lack of bounds checking in the TLV parsing function. The code likely does something like:

void parse_tlv(uint8_t *data, uint16_t length) {
    uint8_t type = data[0];
    uint16_t len = (data[1] << 8) | data[2];
    uint8_t value[256]; // fixed stack buffer
    memcpy(value, &data[3], len); // no check if len > 256
}

Vulnerable vs. Patched Code

Vulnerable Code (WiNet-SV200.001.00.P027 and earlier):

void parse_tlv(uint8_t *data, uint16_t length) {
    uint8_t type = data[0];
    uint16_t len = (data[1] << 8) | data[2];
    uint8_t value[256]; // stack buffer
    memcpy(value, &data[3], len); // overflow if len > 256
}

Patched Code (Hypothetical):

void parse_tlv(uint8_t *data, uint16_t length) {
    uint8_t type = data[0];
    uint16_t len = (data[1] << 8) | data[2];
    if (len > 256) {
        // error handling, reject message
        return;
    }
    uint8_t value[256];
    memcpy(value, &data[3], len);
}

No official patch is available as of this report.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A SunGrow WiNet-SV200 device with firmware <= WiNet-SV200.001.00.P027.
• Network access to the device's MQTT port (default 1883 or 8883 for TLS).
• Knowledge of the MQTT topic and encryption key (may be hardcoded or derived from device serial).

Exploitation Steps:

1. Reconnaissance: Scan for SunGrow devices using Shodan dorks: "SunGrow WiNet" or "WiNet-SV200".
2. Connect to MQTT: Use an MQTT client (e.g., mosquitto_pub) to connect to the device.
3. Craft Payload: Create a malicious MQTT message with a TLV field where the Length is set to a large value (e.g., 0xFFFF) and the Value contains shellcode.
4. Send Payload: Publish the message to the appropriate topic (e.g., solar/config).
5. Trigger Overflow: The device parses the TLV, overflows the stack, and executes the shellcode.

Example Payload (Python):

import struct
import paho.mqtt.client as mqtt

def exploit():
    client = mqtt.Client()
    client.connect("192.168.1.100", 1883, 60)
    # Craft TLV: Type=0x01, Length=0xFFFF, Value=shellcode
    shellcode = b"\x90" * 1000  # placeholder
    tlv = struct.pack("!BH", 0x01, 0xFFFF) + shellcode
    client.publish("solar/config", tlv)
    client.disconnect()

Note: No public exploit code is available. The above is a conceptual example.

Blue Team (Defense & Detection)

Detection:

• Monitor MQTT traffic for unusually large payloads (e.g., TLV Length > 256 bytes).
• Deploy network-based IDS rules (see Suricata below).
• Enable logging on the device (if possible) to capture crash dumps.

Mitigation:

• Isolate SunGrow devices on a separate VLAN with strict firewall rules.
• Disable MQTT if not required.
• Monitor for firmware updates from SunGrow.

Indicators of Compromise (IOCs)

• Network IOCs:
  • MQTT packets with TLV Length field > 256 bytes.
  • Connections to unknown MQTT brokers from the device.
  • Unusual outbound connections from the device (e.g., to IPs not in the SunGrow cloud).
• Host IOCs:
  • Device crash logs indicating stack overflow.
  • Unexpected processes running on the device (if accessible).
  • Modified firmware or configuration files.
• File IOCs:
  • None specific, as this is a memory corruption vulnerability.

Detection Engineering

YARA Rule

rule CVE_2024_50697_MQTT_TLV_Overflow {
    meta:
        description = "Detects MQTT packets with oversized TLV Length field targeting SunGrow WiNet-SV200"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2024-50697"
    strings:
        $tlv_header = { ?? ?? ?? } // Type (1 byte) + Length (2 bytes)
        $large_length = { FF FF } // Length > 256
    condition:
        $tlv_header and $large_length
}

Sigma Rule

title: CVE-2024-50697 SunGrow WiNet-SV200 MQTT TLV Buffer Overflow
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects MQTT packets with oversized TLV Length field
author: Valters IT
logsource:
    category: network
    product: suricata
detection:
    selection:
        event_type: alert
        alert.signature_id: 3000001
    condition: selection
falsepositives:
    - Legitimate large MQTT messages (unlikely)
level: high

Suricata Rule

alert tcp any any -> any 1883 (msg:"CVE-2024-50697 SunGrow WiNet-SV200 MQTT TLV Buffer Overflow"; flow:to_server,established; content:"|00 00|"; depth:2; byte_test:2,>,256,2; sid:3000001; rev:1;)

Note: This rule assumes the TLV Length field is at offset 2 in the MQTT payload. Adjust based on actual protocol specifics.

Remediation & Mitigation

Immediate Actions:

1. Disable MQTT: If not required, disable the MQTT service on the device.
2. Network Segmentation: Place SunGrow devices on a separate VLAN with strict ACLs.
3. Monitor: Deploy the above detection rules to monitor for exploitation attempts.

Long-Term Actions:

1. Firmware Update: Await an official patch from SunGrow. Contact SunGrow support for updates.
2. Replace Device: If no patch is forthcoming, consider replacing the device with a patched alternative.
3. Vendor Disclosure: If you have a relationship with SunGrow, report the vulnerability to accelerate patching.

Workaround: If MQTT is required, use a proxy that validates TLV lengths before forwarding to the device.

Valters IT
Securing Digital Frontiers