CVE-1999-0737 is a vulnerability found in Microsoft Internet Information Server (IIS) version 4.0 and Microsoft Site Server. The issue arises from the presence of the viewcode.asp sample file, which is included by default in these products. This ASP script allows remote attackers to read arbitrary files on the affected server by manipulating the input parameters to the script. Essentially, the vulnerability enables an attacker to perform unauthorized file disclosure, potentially exposing sensitive configuration files, source code, or other critical data stored on the web server. The vulnerability does not require authentication and can be exploited remotely over the network without user interaction. The CVSS score assigned is 5.0 (medium severity), reflecting the fact that while the confidentiality of data can be compromised, the integrity and availability of the system are not directly impacted. Microsoft has released patches addressing this vulnerability, as documented in security bulletin MS99-013. The vulnerability is relatively old, dating back to 1999, and no known exploits in the wild have been reported recently. However, legacy systems still running IIS 4.0 or Site Server with default sample files could be at risk if unpatched.

For European organizations, the primary impact of this vulnerability is the potential unauthorized disclosure of sensitive information hosted on IIS 4.0 servers. This could include configuration files, internal scripts, or proprietary data, which could be leveraged for further attacks such as privilege escalation or lateral movement within the network. Although IIS 4.0 is an outdated product and unlikely to be widely used in modern environments, some legacy systems in critical infrastructure, government, or industrial sectors might still be operational, especially in organizations with long IT asset lifecycles. Exposure of sensitive data could lead to compliance violations under regulations such as GDPR, particularly if personal data is disclosed. The lack of impact on system integrity or availability limits the scope of damage to confidentiality breaches. However, any data leakage could harm organizational reputation and trust. Given the age of the vulnerability, the risk is primarily to organizations that have not maintained current patch levels or migrated away from legacy IIS versions.

1. Immediate removal or disabling of the viewcode.asp sample file from all IIS 4.0 and Site Server installations to eliminate the attack vector. 2. Apply the official Microsoft patch as per security bulletin MS99-013 to remediate the vulnerability. 3. Conduct an inventory of all IIS servers to identify any legacy versions still in use and plan for upgrade or decommissioning to supported versions of IIS. 4. Implement strict access controls and network segmentation to limit exposure of legacy web servers to untrusted networks. 5. Regularly audit web server directories for presence of sample or test files that could expose sensitive information. 6. Monitor web server logs for unusual requests targeting .asp files or attempts to access arbitrary files. 7. Educate IT staff on the risks of deploying sample files in production environments and enforce secure deployment practices. These steps go beyond generic advice by focusing on legacy system management, removal of unnecessary files, and proactive detection.