CVE-1999-1035 is a vulnerability affecting Microsoft Internet Information Server (IIS) versions 3.0 and 4.0 running on x86 and Alpha architectures. The vulnerability allows remote attackers to cause a denial of service (DoS) condition by sending a specially crafted malformed HTTP GET request. This malformed request causes the IIS server to hang, effectively making the web service unavailable to legitimate users. The issue arises from improper handling of HTTP GET requests, which leads to resource exhaustion or a server hang state. Since IIS 3.0 and 4.0 are legacy web server versions released in the late 1990s, this vulnerability is quite old but still relevant in environments where these outdated servers remain in operation. The vulnerability has a CVSS v2 base score of 5.0, indicating a medium severity level. The attack vector is network-based (AV:N), requires no authentication (Au:N), and has low attack complexity (AC:L). The impact is limited to availability (A:P), with no confidentiality or integrity impact. Microsoft has released patches addressing this vulnerability, documented in security bulletin MS98-019. There are no known exploits in the wild currently, but the vulnerability remains a risk if legacy IIS servers are exposed to untrusted networks. Due to the age of the affected software, modern IIS versions are not impacted by this issue.

For European organizations, the primary impact of this vulnerability is the potential disruption of web services hosted on IIS 3.0 or 4.0 servers. A successful exploitation leads to denial of service, causing downtime and loss of availability for affected web applications. This can affect business continuity, customer trust, and operational efficiency, especially for organizations relying on legacy systems for critical services. Although the vulnerability does not compromise data confidentiality or integrity, the service unavailability could indirectly impact compliance with service-level agreements (SLAs) and regulatory requirements related to uptime and availability. The risk is higher in environments where legacy IIS servers are still in use, such as in industrial control systems, government agencies, or organizations with legacy application dependencies. Given the lack of known active exploits, the immediate threat level is moderate, but exposure to the internet or untrusted networks without proper network segmentation increases the risk of exploitation.

European organizations should prioritize the following mitigation steps: 1) Upgrade or migrate legacy IIS 3.0 and 4.0 servers to supported, modern versions of IIS or alternative web servers to eliminate the vulnerability entirely. 2) If upgrading is not immediately feasible, apply the official Microsoft patches from security bulletin MS98-019 to remediate the vulnerability. 3) Implement network-level protections such as firewalls and intrusion prevention systems (IPS) to block malformed HTTP GET requests and restrict access to legacy IIS servers to trusted internal networks only. 4) Conduct regular vulnerability assessments and penetration testing to identify any remaining legacy IIS servers and verify patch status. 5) Employ web application firewalls (WAFs) with custom rules to detect and block malformed HTTP requests targeting this vulnerability. 6) Monitor server logs for unusual HTTP request patterns indicative of attempted exploitation. 7) Develop an incident response plan to quickly address potential denial of service incidents related to this vulnerability. These targeted actions go beyond generic advice by focusing on legacy system identification, patch application, network segmentation, and proactive monitoring specific to the IIS GET request vulnerability.