CVE-2021-22945 in macOS
Summary
by MITRE • 09/24/2021
When sending data to an MQTT server, libcurl
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Analysis
by VulDB Data Team • 06/09/2025
CVE-2021-22945 represents a vulnerability in libcurl that affects the handling of MQTT server communications, specifically related to the MQTT protocol implementation within the cURL library. This vulnerability stems from improper validation of MQTT packet structures during data transmission to MQTT servers, creating potential attack vectors that could be exploited by malicious actors. The flaw occurs when libcurl processes MQTT protocol data, particularly in scenarios where the library receives or sends MQTT packets containing malformed or specially crafted data structures.
The technical root cause of this vulnerability lies in the insufficient input validation mechanisms within libcurl's MQTT implementation. When the library processes MQTT communication, it fails to properly validate the structure and content of MQTT packets before attempting to parse or transmit them. This inadequate validation allows attackers to craft malicious MQTT packets that could trigger unexpected behavior in the vulnerable libcurl implementation. The vulnerability is classified under CWE-20, which addresses improper input validation, and specifically relates to protocol implementation flaws in network communication libraries. The flaw enables a range of potential attacks including buffer overflows, memory corruption, or denial of service conditions that could disrupt normal MQTT server operations.
From an operational impact perspective, this vulnerability poses significant risks to systems that rely on libcurl for MQTT communications, particularly in IoT environments, industrial control systems, and enterprise messaging infrastructure. Attackers could exploit this weakness to disrupt MQTT services, potentially causing service outages or unauthorized data access within networks that depend on MQTT for communication. The vulnerability affects any application or system that utilizes libcurl's MQTT capabilities, making it particularly concerning for organizations with extensive IoT deployments or MQTT-based messaging systems. The attack surface expands when considering that many applications and services use libcurl as their underlying HTTP and MQTT client library, creating widespread potential impact across various networked systems.
Mitigation strategies for CVE-2021-22945 should prioritize immediate patching of affected libcurl versions, with administrators monitoring for security updates from their distribution vendors. Organizations should implement network segmentation and access controls to limit exposure of MQTT services to untrusted networks, while also considering the deployment of intrusion detection systems that can monitor for anomalous MQTT traffic patterns. Security teams should conduct comprehensive vulnerability assessments across their infrastructure to identify systems using vulnerable libcurl versions, particularly focusing on IoT devices, industrial systems, and applications that handle MQTT communications. The ATT&CK framework categorizes this type of vulnerability under T1210 - Exploitation of Remote Services, and T1071.004 - Application Layer Protocol: DNS, as attackers may leverage such vulnerabilities to establish persistent access or conduct reconnaissance activities within affected networks. Additionally, implementing proper input validation at multiple layers of the communication stack, including MQTT broker implementations, can provide defense-in-depth protection against exploitation attempts targeting this specific vulnerability.