CVE-2021-20587 — mitsubishielectric / ezsocket
Out-of-bounds WriteHeap-based buffer overflow vulnerability in Mitsubishi Electric FA Engineering Software (CPU Module Logging Configuration Tool versions 1.112R and prior, CW Configurator versions 1.011M and prior, Data Transfer versions 3.44W and prior, EZSocket versions 5.4 and prior, FR Configurator all versions, FR Configurator SW3 all versions, FR Configurator2 versions 1.24A and prior, GT Designer3 Version1(GOT1000) versions 1.250L and prior, GT Designer3 Version1(GOT2000) versions 1.250L and prior, GT SoftGOT1000 Version3 versions 3.245F and prior, GT SoftGOT2000 Version1 versions 1.250L and prior, GX Configurator-DP versions 7.14Q and prior, GX Configurator-QP all versions, GX Developer versions 8.506C and prior, GX Explorer all versions, GX IEC Developer all versions, GX LogViewer versions 1.115U and prior, GX RemoteService-I all versions, GX Works2 versions 1.597X and prior, GX Works3 versions 1.070Y and prior, iQ Monozukuri ANDON (Data Transfer) versions 1.003D and prior, iQ Monozukuri Process Remote Monitoring (Data Transfer) versions 1.002C and prior, M_CommDTM-HART all versions, M_CommDTM-IO-Link versions 1.03D and prior, MELFA-Works versions 4.4 and prior, MELSEC WinCPU Setting Utility all versions, MELSOFT EM Software Development Kit (EM Configurator) versions 1.015R and prior, MELSOFT Navigator versions 2.74C and prior, MH11 SettingTool Version2 versions 2.004E and prior, MI Configurator versions 1.004E and prior, MT Works2 versions 1.167Z and prior, MX Component versions 5.001B and prior, Network Interface Board CC IE Control utility versions 1.29F and prior, Network Interface Board CC IE Field Utility versions 1.16S and prior, Network Interface Board CC-Link Ver.2 Utility versions 1.23Z and prior, Network Interface Board MNETH utility versions 34L and prior, PX Developer versions 1.53F and prior, RT ToolBox2 versions 3.73B and prior, RT ToolBox3 versions 1.82L and prior, Setting/monitoring tools for the C Controller module (SW4PVC-CCPU) versions 4.12N and prior, and SLMP Data Collector versions 1.04E and prior) allows a remote unauthenticated attacker to cause a DoS condition on the software products, and possibly to execute a malicious code on the personal computer running the software products although it has not been reproduced, by spoofing MELSEC, GOT or FREQROL and returning crafted reply packets.
- https://jvn.jp/vu/JVNVU92330101
- https://jvn.jp/vu/JVNVU92330101/index.html
- https://us-cert.cisa.gov/ics/advisories/icsa-21-049-02
- https://www.cisa.gov/news-events/ics-advisories/icsa-21-049-02
- https://www.mitsubishielectric.com/en/psirt/vulnerability/pdf/2020-021_en.pdf
- https://www.mitsubishielectric.com/psirt/vulnerability/pdf/2020-021_en.pdf
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Frequently Asked Questions
A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.
CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.
A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.
Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.
Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.
SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.