CVE-2001-0643 in Internet Explorer
Summary
by MITRE
Internet Explorer 5.5 does not display the Class ID (CLSID) when it is at the end of the file name, which could allow attackers to trick the user into executing dangerous programs by making it appear that the document is of a safe file type.
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Analysis
by VulDB Data Team • 03/28/2025
The vulnerability described in CVE-2001-0643 represents a significant client-side security flaw in Internet Explorer 5.5 that exploited user trust in file type identification mechanisms. This issue specifically targeted the browser's handling of ActiveX controls and their associated Class Identifiers, which are crucial components for executing potentially dangerous code within web environments. The flaw emerged from the browser's insufficient validation of file names and their associated CLSIDs, creating a window of opportunity for attackers to manipulate user perception during file execution processes.
The technical nature of this vulnerability stems from Internet Explorer's improper display of CLSIDs when they appeared at the end of file names, which directly relates to CWE-200, Information Exposure, and CWE-611, Improper Restriction of XML External Entity Reference. When a malicious file was named with a legitimate extension but contained a hidden CLSID at its end, the browser failed to properly inform users about the actual nature of the file being executed. This behavior created a scenario where users might see a file with a seemingly safe extension like .doc or .xls but could unknowingly be executing malicious code through an ActiveX control with a hidden CLSID.
The operational impact of this vulnerability was substantial as it enabled sophisticated social engineering attacks that could bypass user security awareness and trust in file type associations. Attackers could craft file names that appeared legitimate while concealing dangerous execution mechanisms, making it particularly effective against users who relied on visual cues for file safety assessment. This vulnerability directly maps to ATT&CK technique T1203, Exploitation for Client Execution, and T1059, Command and Scripting Interpreter, as it allowed attackers to execute malicious code through compromised user trust in file extensions. The attack vector was particularly dangerous because it leveraged the browser's default behavior of not warning users about the presence of hidden CLSIDs, effectively creating a false sense of security.
Mitigation strategies for this vulnerability required multiple layers of protection including browser updates, user education about file extension manipulation, and enhanced security policies that enforced strict validation of file content regardless of file naming conventions. Organizations needed to implement comprehensive security awareness training to help users recognize potentially dangerous file behaviors and establish strict policies around ActiveX control execution. The vulnerability highlighted the importance of defense-in-depth approaches and demonstrated how seemingly minor UI display issues could create significant security risks when combined with user trust behaviors and the inherent risks of ActiveX technology. This issue ultimately contributed to the broader understanding of how client-side vulnerabilities could be exploited through social engineering and the critical importance of validating all file execution contexts rather than relying solely on visual indicators.