CVE-2000-0201 in Internet Explorer
Summary
by MITRE
The window.showHelp() method in Internet Explorer 5.x does not restrict HTML help files (.chm) to be executed from the local host, which allows remote attackers to execute arbitrary commands via Microsoft Networking.
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Analysis
by VulDB Data Team • 04/21/2026
The vulnerability described in CVE-2000-0201 represents a critical security flaw in Internet Explorer 5.x versions that stems from improper handling of HTML help files. This issue specifically affects the window.showHelp() method which is designed to display help content within web browser environments. The flaw occurs because the method fails to properly validate the source of help files, allowing maliciously crafted HTML help files to be executed from remote locations rather than being restricted to local host execution only. This represents a fundamental breakdown in the browser's security model for handling help content.
The technical nature of this vulnerability aligns with CWE-264, which addresses permissions, privileges, and access controls in software applications. The flaw essentially creates a privilege escalation path where remote attackers can leverage the showHelp() method to execute arbitrary commands on vulnerable systems. When a user visits a malicious webpage that triggers the window.showHelp() method with a remote help file, the browser attempts to execute the content without proper host validation. This allows attackers to exploit the underlying Microsoft Networking infrastructure to gain unauthorized command execution capabilities on target systems. The vulnerability specifically targets the security boundaries that should normally prevent remote code execution through local help file mechanisms.
From an operational impact perspective, this vulnerability presents a severe risk to organizations using Internet Explorer 5.x as their primary browser. Attackers can craft malicious web pages that automatically invoke the showHelp() method with remote help files, potentially leading to complete system compromise. The attack vector leverages the trust relationship between the browser and local help file execution, making it particularly dangerous as users may not realize they are executing malicious code. This vulnerability enables attackers to perform actions such as installing malware, modifying system files, accessing sensitive data, or establishing persistent backdoors on compromised systems. The impact extends beyond individual user sessions to potentially affect entire network infrastructures if multiple users are exposed to the malicious content.
The mitigation strategies for this vulnerability should focus on immediate remediation through software updates and browser security hardening. Organizations must upgrade to newer versions of Internet Explorer that address this specific flaw, as Microsoft released patches to resolve the issue. Network administrators should implement web filtering solutions to block access to potentially malicious help file content and consider disabling the showHelp() method entirely through browser configuration settings. Additionally, users should be educated about the risks of visiting untrusted websites and the importance of keeping their browsers updated. The vulnerability demonstrates the importance of proper input validation and security boundary enforcement in web browser implementations, as outlined in various security frameworks including those referenced in the ATT&CK framework for browser-based attack techniques. Organizations should also implement network segmentation and monitoring to detect suspicious network traffic patterns that may indicate exploitation attempts.