CVE-1999-0736 is a vulnerability found in Microsoft Internet Information Server (IIS) version 4.0 and Site Server, specifically involving the 'showcode.asp' sample file. This ASP script was intended as a demonstration or sample file but contains a security flaw that allows remote attackers to read arbitrary files on the affected server. The vulnerability arises because the showcode.asp file does not properly restrict file access, enabling an attacker to specify arbitrary file paths and retrieve their contents remotely via HTTP requests. This can lead to unauthorized disclosure of sensitive information stored on the server, such as configuration files, source code, or other data that should not be publicly accessible. The vulnerability does not require authentication, and exploitation can be performed remotely over the network with low complexity, as no special privileges or user interaction are needed. The CVSS score assigned is 5.0 (medium severity), reflecting the confidentiality impact without affecting integrity or availability. Microsoft has released patches addressing this vulnerability, as documented in security bulletin MS99-013. No known exploits have been reported in the wild, but the presence of the sample file on production servers poses a risk if left unpatched or unremoved.

For European organizations running legacy IIS 4.0 servers or Site Server installations, this vulnerability could lead to unauthorized disclosure of sensitive internal files, potentially exposing credentials, internal configurations, or proprietary information. Although IIS 4.0 is an outdated product, some legacy systems in critical infrastructure or industrial environments may still be operational in Europe, especially in sectors with long upgrade cycles. The exposure of sensitive data could facilitate further attacks, including targeted intrusions or lateral movement within networks. Confidentiality breaches could lead to regulatory non-compliance under GDPR if personal data is exposed. The vulnerability does not directly impact system integrity or availability, but the information disclosure could indirectly enable more damaging attacks. Given the age of the vulnerability and the availability of patches, the main risk lies in unpatched legacy systems or misconfigured servers still accessible from the internet or internal networks.

European organizations should first identify any IIS 4.0 or Site Server 4.0 instances in their environment, especially those exposed to external networks. Immediate mitigation steps include removing or restricting access to the showcode.asp sample file to prevent arbitrary file reads. Applying the official Microsoft patch MS99-013 is critical to fully remediate the vulnerability. If patching is not feasible due to legacy constraints, organizations should implement network-level controls such as firewall rules or web application firewalls (WAFs) to block access to the vulnerable script. Additionally, conducting regular security audits to detect leftover sample or demonstration files on production servers can prevent similar issues. Monitoring web server logs for suspicious requests targeting showcode.asp or unusual file access patterns can help detect exploitation attempts. Finally, organizations should plan to upgrade legacy IIS versions to supported releases to reduce exposure to known vulnerabilities.