CVE-2002-0823 in Windows
Summary
by MITRE
Buffer overflow in Winhlp32.exe allows remote attackers to execute arbitrary code via an HTML document that calls the HTML Help ActiveX control (HHCtrl.ocx) with a long pathname in the Item parameter.
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Analysis
by VulDB Data Team • 06/25/2025
The vulnerability identified as CVE-2002-0823 represents a critical buffer overflow flaw in the Windows Help system component known as Winhlp32.exe. This executable serves as the core help viewer application in Windows operating systems and is responsible for rendering help files and documentation. The vulnerability specifically manifests when the system processes HTML help files that utilize the HTML Help ActiveX control HHCtrl.ocx. The flaw occurs because the application fails to properly validate input parameters when processing help content, creating an exploitable condition that can be triggered through maliciously crafted HTML documents.
The technical implementation of this vulnerability involves the manipulation of the Item parameter within the HHCtrl.ocx ActiveX control. When an attacker crafts an HTML document containing a specially formatted help request with an excessively long pathname in the Item parameter, the Winhlp32.exe process attempts to process this input without adequate bounds checking. This lack of input validation causes the buffer allocated for storing the pathname parameter to overflow, potentially overwriting adjacent memory locations including return addresses and executable code segments. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, which is a well-documented weakness in software development practices that allows for arbitrary code execution.
The operational impact of this vulnerability is severe and far-reaching across Windows environments. Attackers can leverage this flaw to execute arbitrary code with the privileges of the user running the help viewer application, typically resulting in system compromise. The attack vector is particularly dangerous because it can be delivered through web-based content or email attachments containing malicious help files, making it an attractive target for remote exploitation. This vulnerability affects multiple versions of Windows including Windows 2000, Windows XP, and Windows Server 2003, creating a substantial attack surface across enterprise networks where these systems remain operational. The exploitation of this vulnerability aligns with ATT&CK technique T1203, which involves exploiting software vulnerabilities to gain unauthorized access to systems.
Mitigation strategies for this vulnerability require immediate action from system administrators and security teams. The most effective approach involves applying the security patches released by Microsoft as part of their regular security updates, specifically addressing the Winhlp32.exe buffer overflow issue. Organizations should also implement network segmentation and access controls to limit exposure of systems to potentially malicious content, while disabling unnecessary ActiveX controls and help file processing capabilities. Additionally, security monitoring should be enhanced to detect suspicious help file processing activities and unusual memory access patterns that may indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and memory management practices in system components, reinforcing the need for comprehensive security testing and code review processes that align with industry best practices for preventing buffer overflow exploits.