CVE-2002-0693 in Windows
Summary
by MITRE
Buffer overflow in the HTML Help ActiveX Control (hhctrl.ocx) in Microsoft Windows 98, 98 Second Edition, Millennium Edition, NT 4.0, NT 4.0 Terminal Server Edition, Windows 2000, and Windows XP allows remote attackers to execute code via (1) a long parameter to the Alink function, or (2) script containing a long argument to the showHelp function.
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Analysis
by VulDB Data Team • 06/25/2025
The vulnerability described in CVE-2002-0693 represents a critical buffer overflow flaw within the HTML Help ActiveX Control component known as hhctrl.ocx which was prevalent across multiple Microsoft Windows operating systems including Windows 98, 98 Second Edition, Millennium Edition, NT 4.0, NT 4.0 Terminal Server Edition, Windows 2000, and Windows XP. This particular vulnerability resides in the ActiveX control's handling of user-supplied input parameters, specifically targeting two distinct functions that process help system requests. The flaw manifests when the control receives excessively long parameter values, creating conditions where memory boundaries are exceeded and potentially allowing malicious code execution. The vulnerability is categorized under CWE-121 as a stack-based buffer overflow, which occurs when a program writes data beyond the allocated buffer space on the stack, often leading to arbitrary code execution.
The technical exploitation of this vulnerability occurs through two primary attack vectors that leverage the control's Alink and showHelp functions. Attackers can trigger the buffer overflow by providing a lengthy parameter string to the Alink function, or by crafting malicious scripts containing extended arguments for the showHelp function. When these functions process the oversized input data, they fail to properly validate the length of the supplied parameters, allowing the data to overwrite adjacent memory locations. This memory corruption can be manipulated to redirect program execution flow, potentially allowing attackers to inject and execute malicious code with the privileges of the user running the affected application. The attack can be executed remotely through web pages or other network-delivered content, making it particularly dangerous in web browsing environments where users might unknowingly encounter malicious content.
The operational impact of this vulnerability extends beyond simple privilege escalation as it provides attackers with complete system compromise capabilities across the affected Windows platforms. Since the vulnerability affects the core HTML Help system that was widely deployed across various Windows versions, the attack surface is extensive and the exploitation potential is high. The buffer overflow can be leveraged to execute arbitrary code, potentially leading to full system compromise, data theft, or the installation of persistent backdoors. This vulnerability directly aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1068 for Exploitation for Privilege Escalation, as attackers can use the overflow to gain elevated privileges and establish persistent access to compromised systems. The vulnerability's presence in ActiveX controls makes it particularly dangerous in corporate environments where ActiveX components are commonly enabled and used for various applications and web content delivery.
Mitigation strategies for CVE-2002-0693 should focus on both immediate remediation and long-term security hardening approaches. Microsoft released security patches and updates for affected Windows versions to address this vulnerability, and organizations should ensure all systems are updated with the latest security patches. Additionally, implementing security measures such as disabling ActiveX controls in web browsers, configuring browser security settings to restrict ActiveX behavior, and employing application whitelisting can significantly reduce exploitation risks. Network-based protections including firewall rules that block access to potentially malicious content and intrusion detection systems that monitor for exploitation attempts should be deployed. Organizations should also consider implementing sandboxing techniques for web browsing activities and regularly monitoring system logs for suspicious activity related to help system access or ActiveX control usage. The vulnerability serves as a classic example of why proper input validation and memory management practices are essential in software development, particularly for components that handle user-supplied data in system-critical applications.