CVE-2000-0149 is a medium-severity vulnerability affecting multiple versions of the Zeus web server, specifically versions 3.1.1 through 3.1.9 and 3.3 through 3.3.5. The vulnerability arises because the Zeus web server improperly handles URLs containing a null character (%00) appended at the end. This flaw allows remote attackers to bypass normal processing and view the source code of CGI (Common Gateway Interface) programs hosted on the server. Normally, CGI scripts are executed server-side, and only their output is sent to the client. However, due to this vulnerability, an attacker can retrieve the raw source code of these scripts, potentially exposing sensitive information such as embedded credentials, database queries, or business logic. The vulnerability requires no authentication and can be exploited remotely over the network with low complexity, as it only involves appending a null character to a URL. The CVSS score of 5.0 reflects a medium severity, primarily due to the confidentiality impact (disclosure of source code) without affecting integrity or availability. No patch is available for this vulnerability, and there are no known exploits in the wild, likely due to the age of the vulnerability and the obsolescence of the Zeus web server product. However, the risk remains for legacy systems still running these affected versions.

For European organizations, the primary impact of this vulnerability is the potential exposure of sensitive source code for web applications running on vulnerable Zeus web servers. Disclosure of source code can lead to further attacks, including exploitation of embedded credentials, logic flaws, or other vulnerabilities within the CGI scripts. This can compromise confidentiality and potentially lead to unauthorized access to backend systems or data breaches. While the vulnerability does not directly affect system integrity or availability, the information leakage can facilitate more severe attacks. Organizations relying on legacy Zeus web servers, especially in sectors with sensitive data such as finance, healthcare, or government, face increased risk. Additionally, compliance with data protection regulations like GDPR could be jeopardized if sensitive personal data is exposed as a result of this vulnerability. Given the lack of patches, affected organizations must consider alternative mitigations or migration strategies to reduce risk.

Since no official patch is available for this vulnerability, European organizations should implement compensating controls to mitigate risk. These include: 1) Disabling or removing CGI scripts on Zeus web servers where possible, or migrating them to more secure and supported platforms. 2) Implementing strict input validation and URL filtering at the web server or network perimeter to block requests containing null characters (%00). 3) Employing web application firewalls (WAFs) configured to detect and block suspicious URL patterns indicative of this attack. 4) Restricting access to the web server to trusted networks or VPNs to reduce exposure. 5) Conducting thorough code reviews and audits of CGI scripts to identify and remediate sensitive information that should not be exposed. 6) Planning for decommissioning or upgrading legacy Zeus web servers to modern, supported web server software with active security updates. 7) Monitoring web server logs for anomalous requests containing null characters or attempts to access source code files. These targeted measures go beyond generic advice and address the specific exploitation vector of this vulnerability.