CVE-2025-27473 is a vulnerability classified under CWE-400 (Uncontrolled Resource Consumption) affecting the HTTP.sys component in Microsoft Windows 10 Version 1507 (build 10.0.10240.0). HTTP.sys is a kernel-mode device driver that handles HTTP requests for the Windows operating system, serving as a core part of the HTTP stack. The vulnerability allows an unauthenticated remote attacker to send specially crafted HTTP requests that cause the system to consume excessive resources, such as CPU or memory, leading to a denial of service (DoS) condition. Because the flaw resides in a kernel-mode driver, the impact on system availability can be severe, potentially causing system crashes or making the system unresponsive. The CVSS v3.1 score of 7.5 reflects a high severity due to the ease of exploitation (network attack vector, no privileges or user interaction required) and the significant impact on availability. No confidentiality or integrity impact is noted. The vulnerability affects only the original release of Windows 10 (Version 1507), which is an outdated version no longer supported by Microsoft, meaning no official patches may be available. The lack of known exploits in the wild suggests it is either newly discovered or not yet weaponized, but the potential for DoS attacks remains high. The vulnerability was publicly disclosed on April 8, 2025, with reservation dating back to February 26, 2025. Given the critical role of HTTP.sys in handling web traffic and services, this vulnerability could disrupt web servers, APIs, or other HTTP-based services running on affected systems.

For European organizations, the primary impact of CVE-2025-27473 is the risk of denial of service attacks that can disrupt critical services relying on Windows 10 Version 1507. This includes web servers, internal applications, and network services that utilize HTTP.sys. Service outages could affect business continuity, customer access, and operational processes, especially in sectors such as finance, healthcare, public administration, and critical infrastructure where availability is paramount. Since the vulnerability requires no authentication or user interaction, attackers can launch attacks remotely and anonymously, increasing the threat surface. Organizations still operating legacy Windows 10 systems are particularly vulnerable, as these systems may lack vendor support and security updates. The disruption could also have cascading effects on supply chains and interdependent services. Although no data breach or integrity compromise is expected, the availability impact alone can cause significant operational and reputational damage. European entities with stringent uptime requirements and regulatory obligations around service availability must prioritize addressing this vulnerability.

The most effective mitigation is to upgrade affected systems from Windows 10 Version 1507 to a supported and patched version of Windows 10 or later. Since this version is out of mainstream support, organizations should plan migration strategies to modern OS versions that receive security updates. If upgrading immediately is not feasible, organizations should implement network-level protections such as firewall rules or intrusion prevention systems to restrict or rate-limit incoming HTTP traffic to vulnerable systems, reducing the risk of resource exhaustion. Monitoring HTTP.sys performance metrics and system resource usage can help detect early signs of exploitation attempts. Employing web application firewalls (WAFs) that can identify and block anomalous HTTP requests may also mitigate attack vectors. Additionally, isolating legacy systems from direct internet exposure and using VPNs or secure gateways for remote access can reduce attack surface. Organizations should stay alert for any patches or advisories from Microsoft and apply them promptly. Incident response plans should include procedures for DoS attack detection and mitigation to minimize downtime.