CVE-2026-21250
📋 TL;DR
CVE-2026-21250 is a local privilege escalation vulnerability in Windows HTTP.sys driver where an authorized attacker can exploit untrusted pointer dereference to gain SYSTEM privileges. This affects Windows systems with HTTP.sys enabled, primarily servers and workstations running vulnerable Windows versions. Attackers must already have local user access to exploit this vulnerability.
💻 Affected Systems
- Microsoft Windows
📦 What is this software?
Windows 11 24h2 by Microsoft
Windows 11 24h2 by Microsoft
Windows 11 25h2 by Microsoft
Windows 11 25h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Full SYSTEM privilege compromise allowing complete control over the affected system, installation of persistent malware, credential theft, and lateral movement across the network.
Likely Case
Authorized local user elevates to SYSTEM privileges to install backdoors, modify system configurations, or access sensitive data.
If Mitigated
Limited impact due to proper access controls, network segmentation, and monitoring preventing successful exploitation even if vulnerability exists.
🎯 Exploit Status
Exploitation requires local authenticated access. The CWE-822 (Untrusted Pointer Dereference) suggests relatively straightforward exploitation once initial access is obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: To be determined from Microsoft Security Update
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21250
Restart Required: Yes
Instructions:
1. Check Microsoft Security Update Guide for CVE-2026-21250. 2. Download and install the appropriate security update for your Windows version. 3. Restart the system as required.
🔧 Temporary Workarounds
Disable HTTP.sys if not needed
windowsStop and disable the HTTP service to remove the vulnerable component
sc stop http
sc config http start= disabled
Restrict local user privileges
windowsImplement least privilege for local accounts to reduce attack surface
🧯 If You Can't Patch
- Implement strict access controls to limit who has local login privileges
- Deploy endpoint detection and response (EDR) solutions to monitor for privilege escalation attempts
🔍 How to Verify
Check if Vulnerable:
Check Windows version and installed updates against Microsoft Security Update Guide for CVE-2026-21250Check Version:
systeminfo | findstr /B /C:"OS Name" /C:"OS Version"Verify Fix Applied:
Verify the security update for CVE-2026-21250 is installed via Windows Update history or Get-HotFix PowerShell command📡 Detection & Monitoring
Log Indicators:
- Event ID 4688: New process creation with SYSTEM privileges from non-SYSTEM accounts
- Event ID 4672: Special privileges assigned to new logon
- Unexpected HTTP.sys service crashes or restarts
Network Indicators:
- Unusual outbound connections from previously low-privileged systems
- Lateral movement attempts from compromised systems
SIEM Query:
EventID=4688 AND NewProcessName="*" AND SubjectUserName!="SYSTEM" AND TokenElevationType="%%1936"