CVE-2025-51986 in freemodbus
Summary
by MITRE • 08/14/2025
An issue was discovered in the demo/LINUXTCP implementation of cwalter-at freemodbus v.2018-09-12 allowing attackers to reach an infinite loop via a crafted length value for a packet.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 08/14/2025
The vulnerability identified as CVE-2025-51986 resides within the demo/LINUXTCP implementation of cwalter-at freemodbus version 2018-09-12, representing a critical flaw that can be exploited to induce an infinite loop condition. This issue manifests when attackers craft specific length values within network packets that are processed by the affected implementation, leading to a denial of service scenario where system resources become consumed indefinitely. The vulnerability stems from insufficient input validation and proper boundary checking within the packet processing logic, particularly in how the software handles packet length fields that may contain malicious or malformed values.
The technical implementation flaw occurs in the packet parsing routine where the software does not adequately validate the length parameter of incoming Modbus packets before proceeding with processing. When a crafted packet contains an invalid or excessively large length value, the parsing loop fails to properly terminate, causing the system to enter an infinite loop state. This condition is classified as a CWE-835 loop with no exit condition, which directly violates fundamental software safety principles and can be categorized under ATT&CK technique T1499.301 for network denial of service. The vulnerability affects the core packet handling mechanism in the LINUXTCP implementation, which is responsible for managing network communication in the freemodbus framework.
The operational impact of this vulnerability extends beyond simple service disruption, as it can lead to complete system unresponsiveness and resource exhaustion. Attackers can exploit this flaw by sending specially crafted Modbus packets with manipulated length fields to devices running the vulnerable freemodbus implementation, causing the target system to consume excessive CPU cycles and potentially crash or become unavailable to legitimate users. This vulnerability is particularly concerning in industrial control systems and embedded environments where continuous operation is critical, as it can result in significant operational downtime and potential safety risks. The infinite loop condition can persist until manual intervention occurs, making it difficult to detect and remediate without proper monitoring and alerting mechanisms in place.
Mitigation strategies for CVE-2025-51986 should focus on implementing robust input validation and boundary checking within the packet processing routines. System administrators should ensure that all incoming packet length values are validated against acceptable ranges before processing begins, with proper error handling mechanisms to prevent loop continuation with invalid data. The recommended approach includes implementing maximum length limits for packet processing, adding timeout mechanisms for packet handling operations, and conducting thorough input sanitization. Additionally, network segmentation and intrusion detection systems should be deployed to monitor for anomalous packet patterns that may indicate exploitation attempts. Regular firmware updates and patches should be applied to address this vulnerability, while implementing proper logging and monitoring to detect potential exploitation attempts. The solution aligns with industry best practices for secure coding and follows the principle of least privilege in network communications.