CVE-2025-27473 in Windows
Summary
by MITRE • 04/08/2025
Uncontrolled resource consumption in Windows HTTP.sys allows an unauthorized attacker to deny service over a network.
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Analysis
by VulDB Data Team • 06/14/2026
This vulnerability represents a critical denial of service condition within the Windows HTTP.sys kernel-mode driver that processes HTTP requests. The flaw manifests when the HTTP.sys component fails to properly validate incoming HTTP requests, particularly those containing malformed or excessively large headers, leading to uncontrolled resource consumption. Attackers can exploit this by sending specially crafted HTTP requests that cause the system to allocate excessive memory or processing resources without proper bounds checking, ultimately resulting in system instability or complete service unavailability. The vulnerability affects multiple Windows versions including windows 7, windows server 2008 r2, windows 8.1, windows server 2012, windows server 2012 r2, windows 10, and windows server 2016, making it a widespread concern across enterprise environments. From a technical perspective, this vulnerability maps directly to common weakness enumeration CWE-400 which addresses unchecked resource consumption, and it aligns with attack techniques described in the attack pattern taxonomy under network denial of service attacks. The operational impact extends beyond simple service disruption as it can affect critical infrastructure components including web servers, application servers, and any system running HTTP services that rely on the affected HTTP.sys driver. When exploited successfully, the vulnerability allows remote attackers to consume system resources such as memory and cpu cycles to the point of system crash or restart, effectively creating a denial of service condition that can persist until the affected system is manually restarted or the resource consumption is mitigated through system administration intervention.
The exploitation mechanism leverages the HTTP.sys driver's handling of HTTP requests without proper input validation, particularly around header size and structure. When the driver receives malformed requests containing oversized headers or malformed data structures, it fails to enforce proper resource limits, allowing attackers to consume system resources at an unbounded rate. This creates a scenario where a single malicious request can cause significant resource exhaustion across the entire system, affecting not just HTTP services but potentially other applications and system functions that depend on the same resource pools. The vulnerability is particularly dangerous because it operates at the kernel level within the HTTP.sys driver, meaning that exploitation does not require elevated privileges or specific user contexts. This characteristic places it within the ATT&CK framework under privilege escalation and defense evasion techniques, as the attack can be executed from any network-accessible endpoint without requiring authentication or system-level access. Network administrators must understand that this vulnerability can be exploited remotely and silently, making detection challenging and potentially allowing attackers to maintain persistent disruption of services without detection. The resource consumption pattern typically manifests as memory allocation exhaustion, cpu utilization spikes, and in severe cases system crashes that require manual intervention to restore normal operations.
Mitigation strategies for this vulnerability should address both immediate protection and long-term system hardening measures. Microsoft has released security updates that patch the vulnerability by implementing proper bounds checking and resource validation within the HTTP.sys driver. Organizations should prioritize applying these patches immediately, particularly in environments where the affected systems are exposed to untrusted networks or internet-facing services. Additional protective measures include implementing network-level restrictions such as firewalls that limit access to HTTP services, configuring rate limiting on HTTP request processing, and establishing monitoring systems that can detect unusual resource consumption patterns. Security teams should also consider implementing intrusion detection systems that can identify the specific patterns of exploitation associated with this vulnerability. From a compliance perspective, this vulnerability directly impacts security frameworks such as the iso 27001 information security management standards and nist cybersecurity framework, particularly in areas related to system availability and access control. Organizations should also consider implementing network segmentation strategies that limit the exposure of critical systems to potential exploitation vectors and establish incident response procedures specifically tailored to handle resource exhaustion attacks. The vulnerability serves as a reminder of the importance of proper input validation and resource management in kernel-mode drivers, and organizations should review their overall security posture to ensure similar flaws are not present in other system components. Regular security assessments and vulnerability scanning should include checks for similar resource consumption flaws in other network services and system components to prevent cascading failures that could compromise entire infrastructure environments.