CVE-2021-33175 in X Broker
Summary
by MITRE • 06/08/2021
EMQ X Broker versions prior to 4.2.8 are vulnerable to a denial of service attack as a result of excessive memory consumption due to the handling of untrusted inputs. These inputs cause the message broker to consume large amounts of memory, resulting in the application being terminated by the operating system.
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Analysis
by VulDB Data Team • 06/11/2021
The vulnerability identified as CVE-2021-33175 affects EMQ X Broker versions prior to 4.2.8 and represents a critical denial of service weakness that stems from improper handling of untrusted input data. This flaw manifests when the message broker processes maliciously crafted inputs that trigger excessive memory allocation within the system. The vulnerability falls under the category of resource exhaustion attacks and demonstrates how uncontrolled memory consumption can lead to complete system termination. The affected EMQ X Broker implementations fail to properly validate and sanitize input parameters, allowing attackers to exploit the system's memory management mechanisms. This weakness specifically impacts the broker's ability to handle message processing and connection management, creating a scenario where legitimate operations become impossible due to resource depletion. The issue is particularly concerning in production environments where message brokers serve as critical infrastructure components for real-time communication systems.
The technical implementation of this vulnerability involves the broker's insufficient input validation mechanisms that fail to properly constrain memory allocation during message processing operations. When untrusted inputs are received, the system's memory management routines allocate resources without adequate bounds checking, leading to exponential memory consumption patterns. This behavior creates a memory leak scenario where allocated memory segments grow uncontrollably, eventually exhausting available system resources. The flaw operates at the application level within the message handling pipeline, specifically affecting how the broker processes incoming messages and manages connection state information. Attackers can exploit this by sending specially crafted payloads that cause the broker to continuously allocate memory without proper cleanup or resource limits. The vulnerability is classified as a memory exhaustion issue and maps to CWE-400, which addresses unchecked resource consumption in software applications. The exploitation requires minimal privileges and can be executed remotely, making it particularly dangerous in networked environments where the broker is exposed to untrusted clients.
The operational impact of CVE-2021-33175 extends beyond simple service disruption to encompass complete system instability and potential data loss scenarios. When the memory exhaustion occurs, the operating system's memory management mechanisms typically terminate the affected process to prevent system-wide collapse, resulting in unexpected broker shutdowns. This termination event can disrupt ongoing message flows, cause connection drops for legitimate clients, and potentially lead to message queuing failures. In high-availability environments, such disruptions can trigger failover mechanisms that may introduce additional instability. The vulnerability affects various operational aspects including message throughput, connection handling capabilities, and overall system responsiveness. Organizations using EMQ X Broker in mission-critical applications face significant risk of service degradation or complete outages. The impact is particularly severe in IoT deployments where message brokers handle thousands of concurrent connections and must maintain consistent availability for real-time data processing. The vulnerability also creates opportunities for attackers to perform persistent denial of service attacks that can systematically degrade system performance over time, eventually leading to complete service unavailability.
Mitigation strategies for CVE-2021-33175 primarily focus on upgrading to EMQ X Broker version 4.2.8 or later, which includes proper input validation and memory management improvements. Organizations should implement network segmentation and access controls to limit exposure of the message broker to untrusted networks and clients. Additionally, implementing resource monitoring and alerting systems can help detect abnormal memory consumption patterns before they lead to system termination. The broker should be configured with appropriate memory limits and connection throttling mechanisms to prevent single malicious inputs from consuming excessive resources. Network-level protections such as firewalls and intrusion detection systems can be configured to monitor for suspicious traffic patterns that may indicate exploitation attempts. Regular security assessments and penetration testing should be conducted to identify potential attack vectors and validate the effectiveness of implemented controls. Organizations should also establish incident response procedures specifically addressing message broker resource exhaustion scenarios and maintain backup systems to ensure continued service availability during remediation activities. The vulnerability's exploitation aligns with ATT&CK technique T1499.004, which covers resource exhaustion attacks targeting availability, and organizations should consider implementing defensive measures that address this specific threat vector within their broader security frameworks.