CVE-2025-27473 is a high-severity vulnerability classified under CWE-400, which pertains to uncontrolled resource consumption. This vulnerability affects Microsoft Windows 10 Version 1809, specifically the HTTP.sys component, a kernel-mode device driver that handles HTTP protocol requests. The flaw allows an unauthorized attacker to send specially crafted network requests that cause excessive resource consumption within HTTP.sys, leading to a denial of service (DoS) condition. Since HTTP.sys operates at a low level in the Windows networking stack, exhaustion of its resources can severely impact system availability, potentially causing the affected system to become unresponsive or crash. The vulnerability requires no authentication or user interaction, and can be exploited remotely over the network, making it accessible to a wide range of attackers. The CVSS v3.1 base score of 7.5 reflects the high impact on availability, with no impact on confidentiality or integrity. No known exploits are currently reported in the wild, and no official patches have been linked yet, indicating that mitigation may rely on workarounds or network-level protections until a patch is released.

For European organizations, this vulnerability poses a significant risk to the availability of systems running Windows 10 Version 1809, particularly those exposing HTTP services directly to untrusted networks. Critical infrastructure, public sector services, and enterprises relying on legacy Windows 10 installations could face service disruptions if targeted. The denial of service could interrupt business operations, degrade user experience, and potentially cause cascading failures in dependent systems. Given that Windows 10 Version 1809 is an older release, some organizations may still be using it due to legacy application dependencies or delayed upgrade cycles, increasing their exposure. The lack of authentication requirement and remote exploitability means attackers can launch DoS attacks from anywhere, potentially impacting cloud-hosted services or on-premises servers accessible over the internet. This could also be leveraged as a distraction or component of a multi-stage attack. The absence of known exploits in the wild provides a window for proactive mitigation, but the high severity score demands urgent attention.

European organizations should immediately identify and inventory all systems running Windows 10 Version 1809, especially those exposing HTTP services. Until an official patch is released, network-level mitigations such as filtering or rate-limiting HTTP traffic to vulnerable systems can reduce exposure. Deploying Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) with signatures or heuristics to detect abnormal HTTP request patterns targeting HTTP.sys may help mitigate exploitation attempts. Organizations should accelerate migration plans to supported Windows versions where this vulnerability is not present or has been patched. Regular monitoring of network traffic and system performance indicators can help detect early signs of resource exhaustion. Additionally, segmenting vulnerable systems away from critical infrastructure and restricting inbound HTTP traffic to trusted sources can reduce attack surface. Once a patch becomes available, rapid deployment is essential. Finally, organizations should review and update incident response plans to include scenarios involving HTTP.sys DoS attacks.