CVE-2024-36844 in libmodbus
Summary
by MITRE • 05/31/2024
libmodbus v3.1.6 was discovered to contain a use-after-free via the ctx->backend pointer. This vulnerability allows attackers to cause a Denial of Service (DoS) via a crafted message sent to the unit-test-server.
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Analysis
by VulDB Data Team • 03/12/2025
The vulnerability identified as CVE-2024-36844 affects libmodbus version 3.1.6 and represents a critical use-after-free condition that manifests through the ctx->backend pointer within the library's internal structure. This flaw exists in the unit-test-server component which processes incoming messages, creating a pathway for malicious actors to manipulate the library's memory management behavior. The issue stems from improper handling of memory allocation and deallocation sequences where a pointer reference persists after the memory it points to has been freed, creating a scenario where subsequent operations on that pointer can lead to unpredictable behavior.
The technical implementation of this vulnerability involves the manipulation of message processing within the modbus protocol implementation where the ctx->backend pointer is accessed after being freed during normal operation. When a crafted message is sent to the unit-test-server, it triggers a sequence that leads to the premature deallocation of backend resources while maintaining references to them. This particular flaw falls under the CWE-416 use-after-free category, which is classified as a memory safety issue that can lead to various security implications including denial of service and potentially arbitrary code execution depending on the memory layout and subsequent operations. The vulnerability specifically impacts the modbus communication library's testing infrastructure rather than its core operational components, making it particularly concerning for systems that rely on comprehensive testing procedures.
The operational impact of this vulnerability extends beyond simple denial of service conditions as it can be exploited to disrupt critical infrastructure monitoring and control systems that utilize modbus protocols for communication. The unit-test-server component, while typically used for development and testing purposes, may be accessible in production environments or exposed through misconfigurations, creating a vector for attackers to destabilize systems. This vulnerability can be leveraged to cause persistent service disruption in industrial control systems, building automation systems, and other environments where modbus communication is prevalent. The DoS condition manifests as application crashes or unresponsiveness, potentially leading to extended downtime for systems that depend on continuous modbus communication protocols.
Mitigation strategies for CVE-2024-36844 should focus on immediate patching of affected libmodbus installations to version 3.1.7 or later where the use-after-free condition has been addressed through proper memory management practices. Organizations should implement network segmentation to limit access to unit-test-server components and ensure that only authorized personnel can interact with testing interfaces. Additionally, monitoring systems should be configured to detect unusual message patterns that might indicate exploitation attempts, while regular security assessments should verify that no unauthorized access points exist to modbus testing infrastructure. The vulnerability aligns with ATT&CK technique T1499.004 for network denial of service, and organizations should consider implementing defensive measures that align with the MITRE ATT&CK framework's recommendations for protecting against memory corruption vulnerabilities.