CVE-2021-20608 in GX Works2
Summary
by MITRE • 12/17/2021
Improper Handling of Length Parameter Inconsistency vulnerability in Mitsubishi Electric GX Works2 versions 1.606G and prior allows a remote unauthenticated attacker to cause a DoS condition in GX Works2 by getting GX Works2 to read a tampered program file from a Mitsubishi Electric PLC by sending malicious crafted packets to tamper with the program file.
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Analysis
by VulDB Data Team • 12/24/2021
The CVE-2021-20608 vulnerability represents a critical flaw in Mitsubishi Electric's GX Works2 software version 1.606G and earlier, specifically targeting the improper handling of length parameter inconsistencies within program file processing. This vulnerability exists within the software's file parsing mechanism where the application fails to properly validate or sanitize length parameters when reading program files from Mitsubishi Electric PLCs. The flaw stems from insufficient input validation and error handling procedures that allow maliciously crafted data to bypass normal file integrity checks, creating a pathway for remote exploitation without requiring authentication credentials.
The technical implementation of this vulnerability occurs during the program file reading process where GX Works2 attempts to parse and execute data structures contained within PLC program files. When an attacker sends specially crafted packets containing malformed length parameters, the software's parsing routine becomes confused by the inconsistency between expected and actual data lengths. This inconsistency causes the application to enter an undefined state where it attempts to read beyond allocated memory boundaries or processes corrupted data structures, ultimately leading to a denial of service condition that crashes the GX Works2 application. The vulnerability operates at the application layer and leverages the communication protocols used for PLC program transfers, making it particularly dangerous in industrial control environments where uninterrupted operation is critical.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise industrial automation systems that rely on GX Works2 for programming and configuration activities. Attackers can remotely trigger a denial of service condition that prevents engineers and operators from accessing or modifying PLC programs, effectively halting production processes or preventing emergency system updates. This vulnerability is particularly concerning in manufacturing environments where GX Works2 is used for critical control system management, as the DoS condition can persist until the software is manually restarted or the affected system is rebooted. The lack of authentication requirements means that any remote attacker with network access to the affected system can exploit this vulnerability, making it a significant threat to operational technology infrastructure.
Mitigation strategies for CVE-2021-20608 should prioritize immediate software updates from Mitsubishi Electric to address the root cause of the length parameter handling inconsistency. Organizations should implement network segmentation and access controls to limit exposure of GX Works2 systems to untrusted networks, while also deploying intrusion detection systems that can monitor for suspicious packet patterns associated with this specific vulnerability. The vulnerability aligns with CWE-129, which addresses improper validation of length parameters, and falls under ATT&CK technique T1499.004 for network denial of service, making it a target for both industrial espionage and operational disruption campaigns. Regular security assessments should be conducted to verify that all GX Works2 installations have been properly updated and that network monitoring systems can detect potential exploitation attempts. Additionally, organizations should maintain offline backup procedures for critical PLC programming tasks to ensure operational continuity in case of successful exploitation, while also implementing proper network access controls to prevent unauthorized access to industrial control systems.