CVE-2025-27473 Overview
CVE-2025-27473 is an uncontrolled resource consumption vulnerability in Windows HTTP.sys that allows an unauthorized attacker to deny service over a network. The HTTP.sys kernel-mode driver is a critical Windows component responsible for handling HTTP requests for web servers like IIS, making this vulnerability particularly impactful for organizations running web services on affected Windows systems.
Critical Impact
This denial of service vulnerability affects a wide range of Windows client and server operating systems, from Windows Server 2008 through Windows Server 2025 and Windows 10/11 desktop versions. Successful exploitation can render web services unresponsive without requiring authentication.
Affected Products
- Microsoft Windows 10 (versions 1507, 1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (versions 22H2, 23H2, 24H2)
- Microsoft Windows Server 2008, 2012, 2016, 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- April 8, 2025 - CVE-2025-27473 published to NVD
- July 8, 2025 - Last updated in NVD database
Technical Details for CVE-2025-27473
Vulnerability Analysis
This vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption), indicating a flaw in how HTTP.sys manages system resources when processing HTTP requests. The vulnerability allows remote attackers to exhaust system resources without requiring any form of authentication or user interaction.
HTTP.sys operates in kernel mode and serves as the HTTP listener for Internet Information Services (IIS) and other Windows HTTP-based services. When exploited, the vulnerability causes the kernel driver to consume excessive resources, leading to service degradation or complete denial of service for legitimate users.
The network-based attack vector with low complexity requirements makes this vulnerability particularly dangerous for internet-facing Windows servers hosting web applications or APIs.
Root Cause
The root cause lies in improper resource management within the HTTP.sys kernel driver. The component fails to adequately limit or control resource consumption when handling maliciously crafted or high-volume HTTP requests. This allows attackers to trigger resource exhaustion conditions that impact system availability.
Attack Vector
The attack is executed over the network and does not require authentication, user interaction, or special privileges. An attacker can send specially crafted HTTP requests to a vulnerable Windows system running HTTP.sys-based services, causing the system to exhaust available resources and become unresponsive to legitimate traffic.
The exploitation does not result in data confidentiality or integrity breaches, but focuses exclusively on disrupting service availability—a classic denial of service attack pattern targeting critical infrastructure components.
Detection Methods for CVE-2025-27473
Indicators of Compromise
- Unusual spikes in HTTP.sys resource consumption including memory and CPU utilization
- High volume of HTTP requests from single or multiple external IP addresses targeting Windows web servers
- Service degradation or unresponsiveness of IIS or other HTTP.sys-dependent services
- Windows Event Log entries indicating HTTP.sys driver errors or resource exhaustion
Detection Strategies
- Monitor HTTP.sys performance counters for abnormal resource consumption patterns
- Implement network-level monitoring to detect high-volume HTTP request floods targeting Windows servers
- Configure alerting for IIS application pool failures or service restarts
- Deploy SentinelOne endpoint detection to identify exploitation attempts targeting HTTP.sys
Monitoring Recommendations
- Enable Windows Performance Monitor counters for HTTP Service Request Queues
- Configure network intrusion detection systems to alert on HTTP flood patterns
- Monitor Event Viewer for HTTP.sys kernel driver warnings and errors
- Establish baseline metrics for normal HTTP.sys resource utilization to detect anomalies
How to Mitigate CVE-2025-27473
Immediate Actions Required
- Apply Microsoft security patches for CVE-2025-27473 as soon as possible across all affected Windows systems
- Review network firewall rules to restrict unnecessary HTTP access to internal servers
- Implement rate limiting at network perimeter devices to mitigate DoS attempts
- Consider placing vulnerable servers behind a web application firewall or DDoS mitigation service
Patch Information
Microsoft has released security updates to address this vulnerability. Detailed patch information and download links are available in the Microsoft Security Response Center advisory for CVE-2025-27473. Organizations should prioritize patching internet-facing Windows servers running IIS or other HTTP.sys-dependent services.
Workarounds
- Deploy network-level rate limiting to reduce the impact of potential exploitation attempts
- Configure load balancers to distribute traffic and provide redundancy for critical web services
- Implement IP-based access controls to limit HTTP.sys service exposure to trusted networks
- Consider temporarily disabling HTTP.sys-dependent services on non-essential systems until patches can be applied
# Example: Configure Windows Firewall rate limiting via netsh
netsh advfirewall firewall add rule name="HTTP Rate Limit" dir=in action=allow protocol=TCP localport=80 remoteip=any enable=yes
# Note: Additional rate limiting should be configured at network edge devices
# Consult Microsoft documentation for HTTP.sys configuration options
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
