CVE-1999-0917 is a vulnerability found in the Preloader ActiveX control used by Microsoft Internet Explorer versions 4.0 and 5.0. This ActiveX control allows remote attackers to read arbitrary files on the victim's system. The vulnerability stems from improper access controls within the ActiveX control, enabling attackers to exploit it remotely without requiring authentication or user interaction. By leveraging this flaw, an attacker can craft a malicious web page that, when visited by a user running the vulnerable Internet Explorer versions, can read sensitive files from the user's local file system. This compromises the confidentiality and potentially the integrity of the victim's data. The vulnerability has a CVSS score of 5.1 (medium severity) with the vector AV:N/AC:H/Au:N/C:P/I:P/A:P, indicating that the attack is network-based, requires high attack complexity, no authentication, and impacts confidentiality, integrity, and availability partially. Microsoft has released patches addressing this issue as documented in security bulletin MS99-018. No known exploits have been reported in the wild, likely due to the age of the vulnerability and the obsolescence of the affected Internet Explorer versions. However, legacy systems or environments still running these versions remain at risk.

For European organizations, the impact of CVE-1999-0917 is primarily related to the exposure of sensitive information through unauthorized file reads. Although the affected Internet Explorer versions are very old and largely obsolete, some legacy systems in critical infrastructure, government agencies, or industrial environments may still use them, especially in sectors with slow upgrade cycles. Exploitation could lead to leakage of confidential documents, credentials, or configuration files, potentially facilitating further attacks such as privilege escalation or lateral movement. The partial impact on integrity and availability also suggests that attackers might manipulate or disrupt local files, affecting system stability or data trustworthiness. Given the medium severity and the requirement for high attack complexity, the threat is moderate but should not be ignored in environments where legacy software persists. European organizations with strict data protection regulations (e.g., GDPR) could face compliance risks if sensitive data is exposed due to this vulnerability.

1. Immediate upgrade or replacement of Internet Explorer 4.0 and 5.0 with modern, supported browsers to eliminate exposure to this and other legacy vulnerabilities. 2. Apply the official Microsoft patches from security bulletin MS99-018 on any systems that must continue using these IE versions for legacy application compatibility. 3. Implement network-level controls such as web filtering and firewall rules to block access to malicious or untrusted websites that could host exploit code targeting this vulnerability. 4. Employ endpoint detection and response (EDR) tools to monitor for suspicious ActiveX control usage or unusual file access patterns. 5. Conduct audits to identify and isolate legacy systems still running vulnerable IE versions, and prioritize their upgrade or segmentation from critical networks. 6. Educate users about the risks of visiting untrusted websites, especially on legacy systems. 7. Where legacy systems cannot be upgraded, consider virtualization or sandboxing to contain potential exploitation.