CVE-2021-45933 in wolfMQTT
Summary
by MITRE • 01/01/2022
wolfSSL wolfMQTT 1.9 has a heap-based buffer overflow (8 bytes) in MqttDecode_Publish (called from MqttClient_DecodePacket and MqttClient_HandlePacket).
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Analysis
by VulDB Data Team • 01/05/2022
The vulnerability identified as CVE-2021-45933 represents a critical heap-based buffer overflow in wolfSSL wolfMQTT version 1.9, specifically within the MqttDecode_Publish function. This flaw occurs during the processing of MQTT protocol packets, particularly when handling publish messages that are received by an MQTT client. The buffer overflow manifests as an 8-byte memory corruption issue that can be exploited to potentially execute arbitrary code or cause denial of service conditions. The vulnerability is triggered when the MQTT client processes malformed or specially crafted publish packets that exceed expected buffer boundaries during decoding operations.
The technical implementation of this vulnerability stems from inadequate input validation and buffer boundary checking within the MQTT packet decoding logic. When MqttDecode_Publish processes incoming MQTT publish messages, it fails to properly validate the length of data fields within the message structure before attempting to copy data into allocated heap buffers. This failure creates a scenario where an attacker can craft a malicious MQTT packet with oversized data fields that cause the decoder to write beyond the allocated buffer boundaries, resulting in the 8-byte heap overflow. The function is invoked from both MqttClient_DecodePacket and MqttClient_HandlePacket, indicating that the vulnerability affects multiple code paths within the MQTT client implementation and increases the attack surface.
The operational impact of this vulnerability is significant as it can be leveraged by remote attackers to compromise systems running vulnerable wolfMQTT implementations. The heap-based nature of the overflow allows for potential memory corruption that could lead to arbitrary code execution, particularly when the vulnerable system processes untrusted MQTT traffic. Systems that rely on MQTT for communication protocols, such as IoT devices, industrial control systems, and messaging infrastructure, are particularly at risk. The vulnerability's exploitation could result in complete system compromise, data exfiltration, or service disruption, making it a critical concern for organizations deploying MQTT-based solutions. The specific 8-byte overflow size suggests that the attack vector may be somewhat constrained but still sufficient to enable memory corruption techniques.
Mitigation strategies for CVE-2021-45933 should prioritize immediate patching of wolfMQTT to version 1.9.1 or later, which contains the necessary fixes for the buffer overflow issue. Organizations should also implement network segmentation and access controls to limit exposure to untrusted MQTT traffic, particularly in environments where MQTT clients process external communications. Input validation should be enhanced at multiple layers to ensure that MQTT packet lengths and data fields are properly verified before processing. The vulnerability aligns with CWE-121, heap-based buffer overflow, and could be categorized under ATT&CK technique T1059 for execution through command injection or memory corruption. Security monitoring should be enhanced to detect unusual MQTT traffic patterns that might indicate exploitation attempts, and regular security assessments should be conducted to identify similar vulnerabilities in MQTT implementations. Additionally, implementing proper memory safety practices including bounds checking and using secure coding standards should be prioritized in future development cycles to prevent similar issues from occurring.