CVE-1999-1397 is a high-severity vulnerability affecting Microsoft Index Server 2.0 running on Internet Information Services (IIS) 4.0. The vulnerability arises because Index Server 2.0 stores physical path information in the Windows registry under the ContentIndex\Catalogs subkey of the AllowedPaths key. The permissions on this registry key are insufficiently restrictive, allowing both local and remote users to read it. This exposure enables attackers to obtain the physical directory paths that are being indexed by the server. Since these paths reveal the underlying directory structure of the web server, an attacker can leverage this information to facilitate further attacks such as directory traversal, information disclosure, or targeted exploitation of known vulnerabilities in specific directories or files. The CVSS score of 7.5 (high) reflects the fact that the vulnerability is remotely exploitable without authentication (AV:N/AC:L/Au:N) and impacts confidentiality, integrity, and availability (C:P/I:P/A:P). Although no patches are available and no known exploits have been reported in the wild, the vulnerability remains a significant risk due to the sensitive nature of the information disclosed and the ease of exploitation.

For European organizations, this vulnerability poses a notable risk especially for those still operating legacy systems with IIS 4.0 and Index Server 2.0, which may be found in industrial, governmental, or legacy enterprise environments. Disclosure of physical directory paths can aid attackers in mapping the internal structure of web servers, increasing the likelihood of successful follow-up attacks such as privilege escalation, data exfiltration, or service disruption. Given the high confidentiality, integrity, and availability impact, exploitation could lead to unauthorized access to sensitive data, modification of critical files, or denial of service. This is particularly concerning for organizations subject to strict data protection regulations such as GDPR, where unauthorized data exposure can lead to regulatory penalties and reputational damage. Although modern environments have largely deprecated IIS 4.0 and Index Server 2.0, some legacy systems may still be in use, especially in sectors with long hardware/software lifecycles.

Since no official patches are available for this vulnerability, European organizations should prioritize the following mitigations: 1) Identify and inventory all systems running IIS 4.0 with Index Server 2.0 to assess exposure. 2) Restrict access to the registry keys containing the physical path information by tightening permissions to allow only trusted administrators. 3) Isolate legacy systems from external networks using network segmentation and firewalls to prevent remote exploitation. 4) Disable or uninstall Index Server 2.0 if it is not required, or upgrade to supported versions of IIS and search services that do not exhibit this vulnerability. 5) Monitor network traffic and system logs for unusual access patterns that could indicate reconnaissance or exploitation attempts. 6) Implement compensating controls such as application-layer firewalls or intrusion detection systems to detect and block attempts to access sensitive registry information remotely.