CVE-2000-0564 is a vulnerability affecting the guestbook CGI program within the ICQ Web Front service for multiple versions of ICQ, including 2000a, 99b, and earlier releases such as 0.99b_1.1.1.1, 0.99b_v.3.19, 98.0a, 99a_2.15build1701, and 99a_2.21build1800. The vulnerability arises from improper handling of the 'name' parameter in a URL request to the guestbook CGI script. Specifically, when a remote attacker sends a URL containing an excessively long 'name' parameter, the service fails to properly validate or limit the input length, leading to a denial of service (DoS) condition. This DoS manifests as the service becoming unresponsive or crashing, thereby disrupting availability. The vulnerability does not impact confidentiality or integrity, as it does not allow data leakage or unauthorized modification. Exploitation requires no authentication and can be performed remotely over the network, making it relatively easy to exploit. However, the affected software versions are quite old and largely obsolete, with no patches available to remediate the issue. No known exploits have been reported in the wild. The CVSS v2 score is 5.0 (medium severity), reflecting the network vector, low attack complexity, no authentication, no confidentiality or integrity impact, and partial availability impact.

For European organizations, the impact of this vulnerability is primarily related to service availability disruptions if they are still operating legacy ICQ Web Front services with the affected guestbook CGI program. Given the age of the software, it is unlikely to be in widespread use in modern enterprise environments. However, niche or legacy systems, particularly in organizations with historical reliance on ICQ for internal or customer communications, could experience denial of service conditions leading to temporary loss of service availability. This could affect communication workflows or customer interaction portals relying on the guestbook feature. The lack of confidentiality or integrity impact reduces the risk of data breaches or manipulation. The absence of patches means organizations cannot remediate the vulnerability through updates, increasing reliance on mitigating controls or decommissioning the affected service. The medium severity rating indicates moderate risk, but the practical impact is limited by the obsolescence of the affected software.

Given that no patches are available for this vulnerability, European organizations should prioritize decommissioning or isolating any legacy ICQ Web Front services running the affected versions. If continued use is necessary, organizations should implement network-level protections such as web application firewalls (WAFs) or intrusion prevention systems (IPS) configured to detect and block HTTP requests with abnormally long 'name' parameters targeting the guestbook CGI endpoint. Rate limiting and input validation proxies can also reduce the risk of DoS by limiting the size and frequency of incoming requests. Monitoring and logging HTTP requests to identify anomalous patterns related to the guestbook CGI can provide early warning of exploitation attempts. Additionally, organizations should conduct asset inventories to identify any residual ICQ Web Front deployments and plan for migration to supported communication platforms. Network segmentation can further isolate vulnerable services from critical infrastructure to minimize impact in case of exploitation.