CVE-1999-1473, known as the "Page Redirect Issue," is a vulnerability affecting Microsoft Internet Explorer versions 3.02 and 4.0. When a user visits a website that redirects the browser to another site, Internet Explorer automatically resends the user's authentication credentials (such as HTTP Basic Authentication headers) to the redirected site without user consent or additional verification. This behavior can lead to unintended credential disclosure if the second site is malicious or compromised. The vulnerability arises from the browser's handling of HTTP redirects and authentication headers, where it fails to distinguish between trusted and untrusted redirect destinations. Although the vulnerability does not allow direct compromise of the browser or system, it exposes sensitive authentication information to potentially malicious third-party sites. The CVSS score of 5.0 (medium severity) reflects that the vulnerability impacts confidentiality but does not affect integrity or availability, requires no authentication, and can be exploited remotely over the network. No patches are available for this issue, likely due to the age of the affected software versions, and there are no known exploits in the wild. Given the obsolete nature of Internet Explorer 3.02 and 4.0, modern systems are not affected, but legacy environments may still be at risk if these browsers are in use.

For European organizations, the primary impact of this vulnerability is the potential leakage of authentication credentials when users access web resources that perform redirects to untrusted or malicious sites. This could lead to unauthorized access to internal or external systems if credentials are reused or if attackers capture session tokens or passwords. Confidentiality of sensitive information is at risk, especially in environments where legacy systems or applications still rely on outdated versions of Internet Explorer. Although the vulnerability does not directly compromise system integrity or availability, the exposure of credentials can facilitate further attacks such as unauthorized data access or lateral movement within networks. Organizations in sectors with strict data protection regulations, such as finance, healthcare, and government, may face compliance risks if credential leakage leads to data breaches. However, the practical impact is limited by the rarity of these browser versions in current use and the absence of known active exploits.

Given that no patches are available for Internet Explorer 3.02 and 4.0, European organizations should prioritize the following mitigation strategies: 1) Upgrade all systems and users to modern, supported browsers that do not exhibit this vulnerability, such as the latest versions of Microsoft Edge, Google Chrome, or Mozilla Firefox. 2) Implement network-level controls to restrict access to legacy systems requiring these browsers, isolating them from sensitive environments. 3) Educate users about the risks of following redirects from untrusted websites and encourage cautious browsing behavior. 4) Where legacy applications mandate the use of these IE versions, consider deploying web proxies or gateway solutions that can sanitize or block redirects to untrusted domains. 5) Enforce strong authentication mechanisms such as multi-factor authentication (MFA) to reduce the impact of credential leakage. 6) Monitor network traffic for unusual authentication header transmissions or suspicious redirect patterns that could indicate exploitation attempts. These targeted mitigations go beyond generic advice by addressing the specific limitations of legacy browsers and the nature of the vulnerability.