CVE-2024-8376: Eclipse Mosquitto Use-After-Free Flaw

CVE-2024-8376 Overview

CVE-2024-8376 is a critical memory corruption vulnerability affecting Eclipse Mosquitto, the popular open-source MQTT message broker widely used in IoT deployments. The vulnerability allows an attacker to trigger memory leaks, segmentation faults, or heap-use-after-free conditions by sending specially crafted sequences of MQTT control packets including CONNECT, DISCONNECT, SUBSCRIBE, UNSUBSCRIBE, and PUBLISH commands.

Critical Impact

Remote attackers can exploit this vulnerability to cause denial of service conditions or potentially achieve further system compromise through heap-use-after-free exploitation in Eclipse Mosquitto deployments up to version 2.0.18a.

Affected Products

• Eclipse Mosquitto versions up to and including 2.0.18a
• IoT systems and deployments using vulnerable Mosquitto broker instances
• MQTT-based infrastructure relying on affected Mosquitto versions

Discovery Timeline

• 2024-10-11 - CVE-2024-8376 published to NVD
• 2024-11-15 - Last updated in NVD database

Technical Details for CVE-2024-8376

Vulnerability Analysis

This vulnerability encompasses multiple memory corruption issues within Eclipse Mosquitto's handling of MQTT protocol messages. The root weakness is classified under CWE-401 (Missing Release of Memory after Effective Lifetime), indicating improper memory management during packet processing. An attacker with network access can exploit these flaws by sending specific sequences of MQTT control packets to a vulnerable Mosquitto broker.

The vulnerability manifests in three distinct failure modes: memory leaking where allocated memory is not properly freed, segmentation faults causing broker crashes, and heap-use-after-free conditions where memory is accessed after being deallocated. The heap-use-after-free variant is particularly concerning as it may allow for more sophisticated exploitation beyond denial of service.

Root Cause

The vulnerability stems from improper memory lifecycle management (CWE-401) within Mosquitto's packet processing logic. When handling rapid sequences of CONNECT, DISCONNECT, SUBSCRIBE, UNSUBSCRIBE, and PUBLISH packets, the broker fails to properly track and release memory allocations. This results in memory resources not being freed after their effective lifetime, leading to memory exhaustion or use-after-free conditions when deallocated memory regions are subsequently accessed.

Attack Vector

The attack vector is network-based and requires low privileges to execute. An attacker must be able to establish MQTT connections to the target Mosquitto broker, after which they can send malicious sequences of protocol packets. The attack does not require user interaction and can be executed remotely against any exposed Mosquitto instance running a vulnerable version.

The exploitation involves sending specific orderings of MQTT control packets that trigger the memory management flaws. For example, rapidly alternating between connection establishment and teardown combined with subscription operations can trigger the heap-use-after-free condition.

For technical details regarding the specific packet sequences and memory handling issues, refer to the GitLab Vulnerability Reports and the official security commit.

Detection Methods for CVE-2024-8376

Indicators of Compromise

• Unexpected Mosquitto broker crashes or restarts, particularly with segmentation fault errors
• Gradual memory consumption increase on systems running Mosquitto, indicating potential memory leak exploitation
• Unusual patterns of MQTT connection and disconnection events from single sources
• Core dumps showing heap corruption or use-after-free memory access violations

Detection Strategies

• Monitor Mosquitto broker logs for abnormal connection/disconnection patterns and unexpected terminations
• Implement network monitoring to detect rapid sequences of MQTT control packets from individual clients
• Deploy memory monitoring tools to detect gradual memory consumption increases in Mosquitto processes
• Configure alerting on broker restarts or crashes to identify potential exploitation attempts

Monitoring Recommendations

• Enable verbose logging in Mosquitto to capture detailed connection lifecycle events
• Implement process monitoring with automatic restart capabilities while investigating root cause
• Monitor system memory utilization and set thresholds for Mosquitto process memory consumption
• Review connection logs for clients exhibiting suspicious rapid connect/disconnect behavior

How to Mitigate CVE-2024-8376

Immediate Actions Required

• Upgrade Eclipse Mosquitto to version 2.0.19 or later immediately
• Review network access controls to limit which clients can connect to MQTT brokers
• Implement rate limiting on MQTT connections to slow potential exploitation attempts
• Monitor broker stability and memory usage for signs of active exploitation

Patch Information

Eclipse Foundation has released version 2.0.19 which addresses this vulnerability. The fix is available in the GitHub Release v2.0.19. The specific commit addressing this vulnerability can be reviewed at the GitHub Commit.

Workarounds

• Restrict network access to Mosquitto brokers using firewall rules to trusted clients only
• Implement connection rate limiting at the network level to prevent rapid packet sequences
• Deploy Mosquitto behind a reverse proxy or load balancer with connection throttling capabilities
• Consider implementing client authentication requirements to limit anonymous access

# Configuration example - Restrict listener to specific interface and require authentication
# Add to mosquitto.conf

# Bind to specific interface instead of all interfaces
listener 1883 127.0.0.1

# Require authentication for all connections
allow_anonymous false
password_file /etc/mosquitto/passwd

# Connection rate limiting (if supported by your deployment)
max_connections 100