CVE-2002-0071 in IIS
Summary
by MITRE
Buffer overflow in the ism.dll ISAPI extension that implements HTR scripting in Internet Information Server (IIS) 4.0 and 5.0 allows attackers to cause a denial of service or execute arbitrary code via HTR requests with long variable names.
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Analysis
by VulDB Data Team • 09/23/2025
The vulnerability identified as CVE-2002-0071 represents a critical buffer overflow flaw within the ism.dll ISAPI extension component of Microsoft Internet Information Server versions 4.0 and 5.0. This specific implementation weakness occurs during the processing of HTR (HTML Tracing) scripting requests, where the software fails to properly validate input lengths when handling variable names in the scripting environment. The affected ISAPI extension serves as a crucial interface between the web server and scripting capabilities, making it a prime target for exploitation by malicious actors seeking to compromise server integrity.
The technical nature of this buffer overflow stems from inadequate bounds checking within the ism.dll module when processing HTR requests containing excessively long variable names. This flaw manifests as a classic stack-based buffer overflow condition where attacker-controlled input exceeds the allocated buffer space, potentially overwriting adjacent memory locations including return addresses and control data. The vulnerability operates at the application layer within the web server's scripting execution environment, leveraging the legitimate HTR file processing functionality to execute malicious payloads. According to CWE-121, this represents a stack-based buffer overflow vulnerability that directly enables arbitrary code execution when exploited successfully.
The operational impact of this vulnerability extends beyond simple denial of service conditions to encompass full system compromise capabilities. Attackers can leverage this weakness to execute arbitrary code with the privileges of the IIS service account, potentially leading to complete server takeover. The vulnerability affects both IIS 4.0 and 5.0 versions, representing a significant security gap in Microsoft's web server implementations during that era. The attack vector requires only a single malicious HTR request with oversized variable names, making exploitation relatively straightforward and accessible to attackers with basic technical knowledge. This vulnerability directly maps to attack techniques described in the MITRE ATT&CK framework under the T1190 category for exploitation of remote services, specifically targeting web server applications.
Mitigation strategies for CVE-2002-0071 involve immediate implementation of security patches provided by Microsoft through their regular security updates, as well as network-level protections such as firewall rules restricting access to HTR file extensions. System administrators should implement input validation controls to limit variable name lengths in HTR files and consider disabling HTR scripting capabilities entirely if not required for business operations. Additionally, implementing proper access controls and network segmentation can limit the potential impact of successful exploitation attempts. The vulnerability highlights the importance of proper input validation and memory management practices in server-side applications, aligning with security best practices outlined in the OWASP Top Ten and other industry standards for secure coding practices. Organizations should also consider migrating away from unsupported IIS versions to receive ongoing security support and protection against similar vulnerabilities.