CVE-2001-0091 in Internet Explorer
Summary
by MITRE
The ActiveX control for invoking a scriptlet in Internet Explorer 5.0 through 5.5 renders arbitrary file types instead of HTML, which allows an attacker to read arbitrary files, aka a variant of the "Scriptlet Rendering" vulnerability.
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Analysis
by VulDB Data Team • 04/07/2017
The vulnerability described in CVE-2001-0091 represents a critical security flaw in Microsoft Internet Explorer versions 5.0 through 5.5 that stems from improper handling of ActiveX controls during scriptlet execution. This vulnerability falls under the category of improper input validation and insecure deserialization patterns, as outlined in CWE-20. The issue specifically affects the way Internet Explorer processes ActiveX controls that invoke scriptlets, creating a pathway for malicious actors to manipulate file rendering behavior. When a user encounters a malicious web page containing a specially crafted ActiveX control, the browser's default rendering mechanism can be subverted to display arbitrary file types rather than the expected HTML content, fundamentally altering the security boundaries of the browser environment.
The technical exploitation of this vulnerability relies on the insecure handling of file types within the ActiveX control invocation chain. When Internet Explorer encounters a scriptlet through an ActiveX control, it should typically render the content as HTML or execute it within a secure scripting context. However, the flaw allows attackers to manipulate the control's behavior to force the browser to render arbitrary file types, potentially including system files, configuration data, or other sensitive information. This misbehavior occurs because the browser's ActiveX processing logic fails to properly validate or sanitize the file types being requested for rendering, creating an information disclosure vector that can be leveraged to read files that should normally be restricted or inaccessible to web-based applications. The vulnerability essentially bypasses the browser's normal security policies that govern file access and rendering.
The operational impact of CVE-2001-0091 is significant and multifaceted, as it enables attackers to perform unauthorized file system access and information disclosure attacks. An attacker could potentially read sensitive files from the local system, including configuration files, user data, or even system-critical information that could be used for further exploitation. This vulnerability particularly affects enterprise environments where Internet Explorer 5.0 through 5.5 was commonly deployed, as it allows for the compromise of user sessions and potential privilege escalation. The attack surface is broad since ActiveX controls were widely used in enterprise web applications, making this vulnerability particularly dangerous in corporate environments where users might encounter malicious content through legitimate business applications or web portals. The vulnerability also aligns with ATT&CK technique T1059.007 for scriptlets and T1566 for social engineering through malicious web content, creating a comprehensive attack pathway that combines multiple exploitation vectors.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security posture improvements. Microsoft released patches to fix the underlying ActiveX control rendering logic, but organizations should also implement comprehensive browser security policies that restrict ActiveX control usage and enforce strict content security policies. Network-based mitigations such as web application firewalls and content filtering systems can help detect and block malicious ActiveX control implementations. Additionally, users should be educated about the risks of downloading and executing ActiveX controls from untrusted sources, as this vulnerability often relies on social engineering techniques to deliver malicious content. The vulnerability highlights the importance of proper input validation and secure coding practices, particularly when dealing with dynamic content execution and file type handling. Organizations should also consider migrating away from legacy Internet Explorer versions that are no longer supported and implement more modern security frameworks that provide better protection against similar classes of vulnerabilities. This vulnerability serves as a historical example of how insecure ActiveX implementations can create persistent security risks that require both immediate patching and long-term architectural improvements to prevent similar issues in contemporary web applications.