CVE-1999-0489 in Internet Explorer
Summary
by MITRE
MSHTML.DLL in Internet Explorer 5.0 allows a remote attacker to paste a file name into the file upload intrinsic control, a variant of "untrusted scripted paste" as described in MS:MS98-013.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-0489 represents a significant security flaw in Microsoft Internet Explorer 5.0's handling of file upload controls through the MSHTML.DLL component. This issue falls under the broader category of input validation and sanitization failures that have long plagued web browsers and their underlying rendering engines. The vulnerability specifically targets the file upload intrinsic control, which is a fundamental component that allows users to select and upload files to web servers through HTML forms. When a remote attacker can manipulate this control through what is termed a "untrusted scripted paste" technique, they gain the ability to bypass normal file selection processes and potentially execute malicious operations.
The technical implementation of this vulnerability stems from inadequate validation of file names within the MSHTML.DLL library, which is responsible for rendering HTML content in Internet Explorer. When a malicious script attempts to programmatically set a file name in an upload control, the browser fails to properly sanitize or validate the input before processing it. This flaw creates an environment where attacker-controlled data can be injected directly into the file upload mechanism, potentially allowing for arbitrary file selection or manipulation. The vulnerability is particularly concerning because it operates at the browser level rather than requiring exploitation of the web server itself, making it a client-side attack vector that can be leveraged across multiple web applications.
The operational impact of this vulnerability extends beyond simple file upload manipulation and can potentially enable more serious attacks such as arbitrary file execution, privilege escalation, or system compromise. An attacker could craft malicious web pages that automatically attempt to upload files to the target system, bypassing normal user interaction requirements. This type of vulnerability is categorized under CWE-20, which deals with "Improper Input Validation," and aligns with the broader ATT&CK framework's T1059.007 technique for "Command and Scripting Interpreter: JavaScript." The attack surface is particularly dangerous because it can be exploited through various means including phishing campaigns, compromised websites, or malicious advertisements that leverage the browser's trust model to execute unauthorized operations.
Mitigation strategies for this vulnerability require a multi-layered approach focusing on both browser configuration and user education. Microsoft addressed this issue through security updates and patches that strengthened input validation within the MSHTML.DLL component. Organizations should implement strict browser security policies that disable or restrict file upload functionality where possible, and deploy web application firewalls that can detect and block suspicious file upload patterns. The vulnerability also highlights the importance of keeping browser software updated and following security best practices such as implementing content security policies and using sandboxing techniques. Additionally, users should be educated about the risks of visiting untrusted websites and the importance of maintaining updated security software to protect against such client-side vulnerabilities that exploit the fundamental trust relationships within web browsers.