CVE-2025-27473
📋 TL;DR
This vulnerability in Windows HTTP.sys allows unauthorized attackers to cause denial of service by consuming excessive resources. It affects Windows systems using HTTP.sys for web services, potentially impacting web servers and applications relying on this component.
💻 Affected Systems
- Windows HTTP.sys
📦 What is this software?
Windows 10 1507 by Microsoft
Windows 10 1507 by Microsoft
Windows 10 1607 by Microsoft
Windows 10 1607 by Microsoft
Windows 10 1809 by Microsoft
Windows 10 1809 by Microsoft
Windows 10 21h2 by Microsoft
Windows 10 22h2 by Microsoft
Windows 11 22h2 by Microsoft
Windows 11 23h2 by Microsoft
Windows 11 24h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete service unavailability for web applications and services using HTTP.sys, potentially affecting multiple dependent systems.
Likely Case
Degraded performance or temporary service interruptions for web services on affected Windows systems.
If Mitigated
Minimal impact with proper network segmentation, rate limiting, and monitoring in place.
🎯 Exploit Status
Unauthenticated network-based attack requiring only network access to vulnerable HTTP.sys endpoints.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft Security Update Guide for specific KB numbers
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-27473
Restart Required: Yes
Instructions:
1. Apply latest Windows security updates from Microsoft
2. Restart affected systems after patch installation
3. Verify patch installation via Windows Update history
🔧 Temporary Workarounds
Network segmentation and filtering
windowsRestrict network access to HTTP.sys endpoints to trusted sources only
Use Windows Firewall: netsh advfirewall firewall add rule name="Block HTTP.sys" dir=in action=block protocol=TCP localport=80,443,8080 remoteip=untrusted-ips
Rate limiting and request throttling
allImplement request rate limiting at network or application level
🧯 If You Can't Patch
- Implement strict network access controls to HTTP.sys endpoints
- Deploy web application firewalls with DoS protection capabilities
🔍 How to Verify
Check if Vulnerable:
Check Windows version and installed updates against Microsoft advisoryCheck Version:
systeminfo | findstr /B /C:"OS Name" /C:"OS Version"Verify Fix Applied:
Verify security update KB number is installed via Windows Update history📡 Detection & Monitoring
Log Indicators:
- Unusual high volume of HTTP requests in IIS logs
- HTTP.sys error events in Windows Event Logs
- Resource exhaustion warnings
Network Indicators:
- Abnormal spike in HTTP traffic to Windows systems
- Repeated connection attempts to HTTP.sys ports
SIEM Query:
source="windows" event_id=* (http OR iis) AND (request_count > threshold OR error_rate > threshold)