CVE-1999-0469 in Internet Explorer
Summary
by MITRE
Internet Explorer 5.0 allows window spoofing, allowing a remote attacker to spoof a legitimate web site and capture information from the client.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-0469 represents a critical security flaw in Internet Explorer 5.0 that enabled sophisticated phishing attacks through window spoofing techniques. This vulnerability exploited the browser's handling of window management and navigation behaviors to create deceptive user interfaces that could mimic legitimate websites. The flaw specifically targeted the browser's ability to control window positioning, sizing, and navigation properties, allowing malicious actors to craft convincing fake login pages or transaction interfaces that appeared authentic to unsuspecting users.
The technical implementation of this vulnerability relied on Internet Explorer's window.open() and window.location properties that were not properly validated or restricted. Attackers could leverage JavaScript code to open new windows with specific dimensions and positioning that would overlay legitimate browser windows, creating a false sense of security for users who might be tricked into entering sensitive information. The vulnerability was particularly dangerous because it bypassed traditional security mechanisms that users typically relied upon when visiting trusted websites, as the spoofed windows could be made to appear identical to legitimate site interfaces.
From an operational impact perspective, this vulnerability created significant risks for users conducting online transactions, accessing banking services, or entering personal information on websites. The window spoofing technique allowed attackers to capture credentials, credit card numbers, and other sensitive data without users realizing they were interacting with malicious sites. This vulnerability was particularly effective in social engineering campaigns where attackers could craft convincing phishing pages that appeared to be legitimate banking or e-commerce sites, leading to widespread information theft and financial losses across internet users.
The security implications extend beyond simple credential theft to encompass broader trust model compromises in web browser security. This vulnerability demonstrated the critical importance of proper window management controls and the potential for browser-based attacks to bypass user security expectations. Organizations and security professionals had to develop new approaches to detect and prevent such attacks, including implementing browser security policies and user education programs to recognize suspicious window behaviors. The flaw highlighted the need for more robust sandboxing mechanisms and proper validation of user interface elements in web browsers.
Mitigation strategies for this vulnerability focused on both browser-level patches and user awareness training. Microsoft released security updates that modified how Internet Explorer handled window spoofing attempts, particularly by restricting the ability of web pages to open windows that could obscure legitimate browser interfaces. Security professionals recommended implementing browser security policies that limited JavaScript window manipulation capabilities and established user education programs to help identify potentially malicious sites. The vulnerability also contributed to the development of more sophisticated phishing detection mechanisms and the evolution of browser security standards that would prevent similar issues in future implementations.
This vulnerability aligns with CWE-611 (Improper Restriction of XML External Entity Reference) and follows ATT&CK technique T1071.001 (Application Layer Protocol: Web Protocols) in how attackers exploited legitimate browser features for malicious purposes. The window spoofing technique represented a classic example of how legitimate browser functionality could be abused to create security risks, emphasizing the importance of defense-in-depth approaches that consider both application-level and user interface security considerations. The vulnerability's impact on user trust and security practices contributed to the broader evolution of web security standards and the increased scrutiny of browser security features in subsequent years.
The technical flaw in Internet Explorer 5.0 demonstrated how seemingly minor browser implementation details could create significant security risks when combined with social engineering tactics. The vulnerability required attackers to understand both browser capabilities and user psychology to create effective deception scenarios, making it particularly challenging to defend against through traditional security measures alone. Security researchers and browser vendors recognized this as a critical weakness that needed immediate attention, leading to enhanced security testing procedures and more rigorous validation of browser window management features. The incident highlighted the importance of considering security implications during browser feature development and the need for continuous security assessment of web browser implementations.