CVE-2025-68699 – CVE-2025-68699 is a NULL pointer dereference vu... (How to Fix)

Q: What is the severity of CVE-2025-68699?

CVE-2025-68699 has a CVSS score of 6.5 (MEDIUM). CVE-2025-68699 is a NULL pointer dereference vulnerability in NanoMQ MQTT Broker that allows remote attackers to crash the broker by sending a malformed shared subscription topic. This affects all systems running NanoMQ version 0.24.6 with shared subscriptions enabled, potentially causing denial of service for MQTT messaging services.

📋 TL;DR

CVE-2025-68699 is a NULL pointer dereference vulnerability in NanoMQ MQTT Broker that allows remote attackers to crash the broker by sending a malformed shared subscription topic. This affects all systems running NanoMQ version 0.24.6 with shared subscriptions enabled, potentially causing denial of service for MQTT messaging services.

💻 Affected Systems

Products:

NanoMQ MQTT Broker

Versions: Version 0.24.6 only

Operating Systems: All platforms running NanoMQ

Default Config Vulnerable: ⚠️ Yes

Notes: Requires shared subscription feature to be used/accessible. All NanoMQ deployments with version 0.24.6 are vulnerable if exposed to untrusted MQTT clients.

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete broker crash leading to denial of service for all connected MQTT clients, disrupting IoT/edge messaging operations until manual restart.

🟠

Likely Case

Broker crash requiring restart, causing temporary service disruption for MQTT messaging applications.

🟢

If Mitigated

No impact if patched or if shared subscriptions are disabled in configuration.

🌐 Internet-Facing: HIGH - Remote unauthenticated exploitation possible via MQTT protocol.

🏢 Internal Only: HIGH - Same exploit path available internally via MQTT connections.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploit requires sending malformed SUBSCRIBE packet with '$share/ab' topic (missing second slash). No authentication needed if broker allows anonymous connections.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 0.24.7

Vendor Advisory: https://github.com/nanomq/nanomq/security/advisories/GHSA-qv5f-c6v2-2f8h

Restart Required: Yes

Instructions:

1. Download NanoMQ 0.24.7 from official repository. 2. Stop current NanoMQ service. 3. Replace binary with patched version. 4. Restart NanoMQ service.

🔧 Temporary Workarounds

Disable shared subscriptions

all

Prevent exploitation by disabling shared subscription feature in configuration

Edit nanomq.conf and set 'shared_subscription = false'

Network filtering

all

Block malformed MQTT packets at network perimeter

Configure firewall/WAF to drop MQTT packets containing '$share/' topics without proper format

🧯 If You Can't Patch

Implement strict MQTT client authentication to prevent untrusted access
Deploy network monitoring to detect and block exploitation attempts

🔍 How to Verify

Check if Vulnerable:

Check NanoMQ version: 'nanomq --version' should show 0.24.6

Check Version:

nanomq --version

Verify Fix Applied:

Verify version is 0.24.7 or later: 'nanomq --version'

📡 Detection & Monitoring

Log Indicators:

Broker crash logs with SIGSEGV
Error messages related to shared subscription parsing
Unexpected broker restarts

Network Indicators:

MQTT SUBSCRIBE packets with malformed '$share/' topics
Broker becoming unresponsive after specific MQTT traffic

SIEM Query:

source="nanomq.log" AND ("SIGSEGV" OR "segmentation fault" OR "shared subscription" AND "error")

📊 Metadata

CVE ID: CVE-2025-68699

CVSS v3 Score: 6.5 (MEDIUM)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

CWE: CWE-476

Published: February 4, 2026

Last Updated: February 5, 2026

🤖 AI-assisted analysis, reviewed for accuracy

🔗 References

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