CVE-2000-0246 is a vulnerability affecting Microsoft Internet Information Services (IIS) versions 4.0 and 5.0, specifically related to the handling of ISAPI (Internet Server Application Programming Interface) extensions when a virtual directory is mapped to a UNC (Universal Naming Convention) share. The vulnerability arises because IIS does not correctly process ISAPI extensions in this configuration, allowing remote attackers to bypass intended access controls and read the source code of ASP (Active Server Pages) and other files stored on the UNC share. This exposure of source code can reveal sensitive information such as business logic, database connection strings, credentials, or other proprietary code, which could be leveraged for further attacks. The vulnerability is classified as a medium severity issue with a CVSS score of 5.0, indicating that it can be exploited remotely without authentication and with low attack complexity, but it does not impact integrity or availability directly. Microsoft has released patches to address this issue, documented in security bulletin MS00-019. No known exploits have been reported in the wild, but the vulnerability remains relevant for legacy systems still running these IIS versions or configurations involving UNC shares.

For European organizations, this vulnerability poses a risk primarily to those still operating legacy IIS 4.0 or 5.0 servers, especially in environments where virtual directories are mapped to UNC shares. The exposure of ASP source code can lead to confidentiality breaches, potentially revealing sensitive business logic and credentials that could facilitate further compromise or data exfiltration. Although the vulnerability does not allow direct remote code execution or denial of service, the information disclosure can be a stepping stone for attackers to escalate privileges or conduct targeted attacks. Organizations in sectors with strict data protection regulations, such as finance, healthcare, and government, could face compliance issues and reputational damage if sensitive code or data is leaked. Given the age of the affected IIS versions, the impact is mitigated by the fact that most organizations have migrated to newer platforms; however, legacy systems in critical infrastructure or industrial environments may still be vulnerable.

To mitigate this vulnerability, European organizations should prioritize patching affected IIS servers by applying the updates provided in Microsoft Security Bulletin MS00-019. If patching is not immediately feasible, organizations should avoid mapping virtual directories to UNC shares or restrict access to such shares through network segmentation and strict access controls. Additionally, auditing IIS configurations to identify and remediate any use of legacy ISAPI extensions or virtual directories pointing to UNC shares is essential. Organizations should also consider migrating from IIS 4.0/5.0 to supported, modern versions of IIS or alternative web servers to eliminate exposure to this and other legacy vulnerabilities. Implementing robust monitoring and logging to detect unusual access patterns to ASP source files can help identify exploitation attempts. Finally, enforcing the principle of least privilege on file shares and ensuring that sensitive source code is not stored in locations accessible via UNC shares can reduce risk.