CVE-2026-20812
📋 TL;DR
This vulnerability allows an authorized attacker to perform tampering attacks against Windows LDAP services over a network. Attackers can manipulate LDAP directory data or operations when they have valid credentials. Organizations using Windows Active Directory or LDAP services are affected.
💻 Affected Systems
- Windows Server
- Windows Active Directory Domain Services
📦 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 compromise of LDAP directory integrity, allowing attackers to modify user permissions, group memberships, or directory data to enable privilege escalation or persistence.
Likely Case
Unauthorized modification of specific directory attributes or objects, potentially enabling lateral movement or data manipulation.
If Mitigated
Limited impact due to network segmentation, strict access controls, and monitoring that detects anomalous LDAP modifications.
🎯 Exploit Status
Exploitation requires authorized access to LDAP service and knowledge of LDAP protocol manipulation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: To be determined from Microsoft Security Update
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20812
Restart Required: Yes
Instructions:
1. Check Microsoft Security Update Guide for CVE-2026-20812. 2. Download appropriate security update for your Windows Server version. 3. Apply update following Microsoft's deployment guidance. 4. Restart affected servers as required.
🔧 Temporary Workarounds
Restrict LDAP Access
windowsLimit LDAP access to only necessary users and systems using network ACLs and authentication controls.
Enable LDAP Signing
windowsRequire LDAP signing to prevent tampering of LDAP traffic.
Set-ADDCCloningExcludedApplicationList -Add "LDAP"
Configure via Group Policy: Computer Configuration > Policies > Windows Settings > Security Settings > Local Policies > Security Options > Domain controller: LDAP server signing requirements
🧯 If You Can't Patch
- Implement strict network segmentation to isolate LDAP services from untrusted networks
- Enhance monitoring of LDAP modification events and implement alerting for suspicious directory changes
🔍 How to Verify
Check if Vulnerable:
Check Windows version and compare against Microsoft's affected versions list for CVE-2026-20812Check Version:
systeminfo | findstr /B /C:"OS Name" /C:"OS Version"Verify Fix Applied:
Verify Windows Update history contains the security update for CVE-2026-20812 and check system version📡 Detection & Monitoring
Log Indicators:
- Unusual LDAP modification events in Windows Security logs (Event ID 4662)
- Multiple failed LDAP bind attempts followed by successful modifications
- LDAP operations from unexpected source IPs or service accounts
Network Indicators:
- Unusual LDAP traffic patterns, especially modification operations
- LDAP requests with malformed or unexpected parameters
SIEM Query:
source="WinEventLog:Security" (EventCode=4662 OR EventCode=5136) AND (ObjectType="%{77CCDC63-0224-4cfc-93A5-5F7F2B8F551C}" OR ObjectType="%{19195a5b-6da0-11d0-afd3-00c04fd930c9}") | stats count by src_ip, user