CVE-2026-20821
📋 TL;DR
This Windows Remote Procedure Call vulnerability allows unauthorized local attackers to access sensitive information from system memory. It affects Windows systems with RPC services enabled, potentially exposing credentials, tokens, or other confidential data to malicious local users.
💻 Affected Systems
- Windows Remote Procedure Call Runtime
📦 What is this software?
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 23h2 by Microsoft
Windows 11 24h2 by Microsoft
Windows 11 25h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise through credential theft leading to lateral movement and privilege escalation across the network.
Likely Case
Unauthorized disclosure of sensitive information such as authentication tokens, session data, or configuration details to local attackers.
If Mitigated
Limited information exposure with proper access controls and network segmentation preventing lateral movement.
🎯 Exploit Status
Requires local access to the target system and knowledge of RPC internals. No public exploits available as of analysis.
🛠️ 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-2026-20821
Restart Required: Yes
Instructions:
1. Open Windows Update settings
2. Check for updates
3. Install all security updates
4. Restart system when prompted
🔧 Temporary Workarounds
Restrict RPC Access
windowsLimit RPC access to authorized users only through Windows Firewall and group policies
netsh advfirewall firewall add rule name="Block RPC" dir=in action=block protocol=TCP localport=135,445,593
netsh advfirewall firewall add rule name="Block RPC" dir=in action=block protocol=UDP localport=135,137,138,445
Enable Network Segmentation
allIsolate systems with RPC services from untrusted networks
🧯 If You Can't Patch
- Implement strict access controls to limit local user privileges
- Monitor for unusual RPC activity and memory access patterns
🔍 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 KB update is installed via 'wmic qfe list' or 'Get-Hotfix' in PowerShell📡 Detection & Monitoring
Log Indicators:
- Unusual RPC client connections
- Failed authentication attempts to RPC services
- Processes accessing sensitive memory regions
Network Indicators:
- Abnormal RPC traffic patterns
- Multiple failed RPC bind attempts
- Unexpected RPC endpoint enumeration
SIEM Query:
EventID=4688 OR EventID=4689 AND ProcessName LIKE "%rpc%" AND CommandLine CONTAINS suspicious_pattern