CVE-1999-1538 is a vulnerability affecting Microsoft Internet Information Server (IIS) version 4.0 that arises during the upgrade process from IIS versions 2 or 3 to version 4. Specifically, the dynamic link library file ism.dll is inadvertently left accessible in the /scripts/iisadmin directory. This file does not enforce access restrictions to the local machine, thereby allowing unauthorized users to access it remotely. Exploiting this vulnerability enables an attacker to retrieve sensitive server information, including the Administrator's password. The vulnerability is rooted in improper cleanup or configuration during the upgrade process, leaving a sensitive component exposed. The CVSS score of 2.1 (low severity) reflects that the attack vector requires local access (AV:L), has low complexity (AC:L), does not require authentication (Au:N), and impacts confidentiality (C:P) but not integrity or availability. No patches are available, and there are no known exploits in the wild, likely due to the age of the vulnerability and the obsolescence of IIS 4.0. However, if legacy systems remain in use, this vulnerability could still be exploited to gain unauthorized access to critical server credentials, potentially leading to further compromise.

For European organizations, the impact of this vulnerability depends largely on whether legacy IIS 4.0 servers remain operational. If such systems are still in use, the exposure of the Administrator's password could lead to unauthorized administrative access, allowing attackers to manipulate web server configurations, deploy malicious scripts, or access sensitive data hosted on the server. This could compromise confidentiality and potentially lead to lateral movement within the network. Given the vulnerability does not affect integrity or availability directly, the immediate impact might be limited to information disclosure. However, the stolen credentials could be leveraged for more severe attacks. European organizations with legacy infrastructure in sectors such as government, manufacturing, or critical infrastructure, where older systems sometimes persist, could face increased risk. Additionally, compliance with GDPR and other data protection regulations means that unauthorized disclosure of credentials and subsequent data breaches could result in legal and financial penalties.

Since no official patches are available for this vulnerability, European organizations should take specific steps to mitigate risk: 1) Identify and inventory any IIS 4.0 servers still in operation, especially those upgraded from IIS 2 or 3. 2) Remove or restrict access to the /scripts/iisadmin directory, specifically the ism.dll file, by applying strict file system permissions or web server access controls to prevent unauthorized access. 3) If possible, decommission legacy IIS 4.0 servers and migrate to supported, updated versions of IIS or alternative web servers with active security support. 4) Implement network segmentation to isolate legacy servers from external and less trusted internal networks, limiting exposure. 5) Monitor logs for any unusual access attempts to the /scripts/iisadmin directory or ism.dll file. 6) Enforce strong password policies and consider changing Administrator passwords on affected servers to reduce the risk of credential compromise. 7) Employ intrusion detection/prevention systems to detect exploitation attempts targeting legacy IIS components.