CVE-2000-0465 is a vulnerability affecting Microsoft Internet Explorer versions 4.0, 5.0, 5.01, and 5.5. The core issue lies in the browser's improper verification of the domain of frames embedded within a browser window. Specifically, Internet Explorer fails to correctly enforce the same-origin policy for frames, which is a fundamental security mechanism designed to prevent scripts or content from one domain from accessing or manipulating content from another domain. Due to this flaw, a remote attacker can craft malicious web pages that embed frames pointing to local client files or other sensitive resources. Because the domain verification is bypassed, the attacker can read the contents of these client files through the frame, leading to unauthorized disclosure of potentially sensitive information stored on the user's machine. This vulnerability impacts confidentiality, integrity, and availability to some extent, as it allows partial reading and potential manipulation of client-side data. The vulnerability is exploitable remotely over the network without requiring user authentication; however, exploitation requires user interaction in the form of visiting a malicious or compromised website. The CVSS v2 base score is 5.1 (medium severity), reflecting the moderate complexity of exploitation (high attack complexity) and the partial impact on confidentiality, integrity, and availability. Microsoft has released patches addressing this vulnerability, as documented in security bulletin MS00-033. No known exploits have been reported in the wild, but the vulnerability's age and the widespread historical use of affected Internet Explorer versions mean that unpatched legacy systems remain at risk. Given the age of the vulnerability, modern browsers are not affected, but legacy systems or environments running outdated software could still be vulnerable.

For European organizations, the impact of CVE-2000-0465 primarily concerns legacy systems still running Internet Explorer 4.x or 5.x, which may be found in industrial control systems, government agencies, or organizations with legacy applications dependent on these browsers. Successful exploitation could lead to unauthorized disclosure of sensitive internal files, potentially exposing confidential business data, personal information, or intellectual property. This could result in reputational damage, regulatory non-compliance (especially under GDPR), and operational disruptions if sensitive configuration or credential files are accessed and manipulated. Although the vulnerability does not allow direct remote code execution, the ability to read client files can facilitate further attacks, such as social engineering or targeted phishing campaigns. The medium severity rating suggests that while the threat is not critical, it remains a significant risk for unpatched legacy environments. European organizations with strict data protection requirements must consider the confidentiality risks, especially in sectors like finance, healthcare, and government where sensitive data is prevalent.

1. Immediate patching: Apply the Microsoft security update MS00-033 to all affected Internet Explorer installations to remediate the vulnerability. 2. Legacy system audit: Conduct a thorough inventory of systems running Internet Explorer 4.x or 5.x and assess their necessity. 3. Browser upgrade or replacement: Where possible, upgrade to modern, supported browsers that do not have this vulnerability. 4. Network segmentation: Isolate legacy systems from the internet and untrusted networks to reduce exposure to remote attacks. 5. Web filtering and content security: Implement strict web filtering policies to block access to untrusted or malicious websites that could exploit this vulnerability. 6. User awareness training: Educate users about the risks of visiting untrusted websites, especially when using legacy browsers. 7. Application whitelisting: Restrict execution of unauthorized scripts or applications that could leverage this vulnerability. 8. Monitor logs and network traffic for unusual frame or cross-domain activity that could indicate exploitation attempts. These steps go beyond generic advice by focusing on legacy system management, network controls, and user behavior tailored to the specific nature of this vulnerability.