CVE-2021-42291
📋 TL;DR
This vulnerability allows authenticated attackers to elevate privileges in Active Directory Domain Services by exploiting improper access control. It affects Windows Server systems running Active Directory Domain Services, potentially enabling attackers to gain domain administrator privileges.
💻 Affected Systems
- Windows Server
📦 What is this software?
Windows Server by Microsoft
Windows Server by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Attackers gain full domain administrator control, allowing them to create/delete accounts, modify security policies, access sensitive data, and persist across the entire domain.
Likely Case
Privileged escalation from standard domain user to domain administrator, enabling lateral movement and credential harvesting across the network.
If Mitigated
Limited impact with proper network segmentation, privileged access management, and monitoring in place, though domain compromise remains possible.
🎯 Exploit Status
Exploitation requires domain user credentials and knowledge of specific Active Directory objects. Public exploit code is available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: November 2021 security updates (KB5007205 for Server 2019, KB5007206 for Server 2022, KB5007192 for Server 2016)
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42291
Restart Required: Yes
Instructions:
1. Apply November 2021 security updates from Windows Update. 2. Restart affected domain controllers. 3. Verify patch installation via 'systeminfo' command.
🔧 Temporary Workarounds
Restrict Active Directory object permissions
windowsApply strict access controls to prevent unauthorized modifications to Active Directory objects
Use Active Directory Administrative Center or PowerShell to review and restrict permissions on sensitive AD objects
🧯 If You Can't Patch
- Implement network segmentation to isolate domain controllers from general user networks
- Enable enhanced auditing and monitoring for Active Directory object modifications
🔍 How to Verify
Check if Vulnerable:
Check if November 2021 security updates are installed via 'systeminfo | findstr /B /C:"KB5007205" /C:"KB5007206" /C:"KB5007192"'Check Version:
systeminfo | findstr /B /C:"OS Name" /C:"OS Version"Verify Fix Applied:
Verify patch installation and check that 'systeminfo' shows the appropriate KB installed📡 Detection & Monitoring
Log Indicators:
- Event ID 4662 with object type 'DS-Replication-Get-Changes' or 'DS-Replication-Get-Changes-All'
- Unusual modifications to Active Directory objects from non-privileged accounts
Network Indicators:
- LDAP traffic patterns showing unusual replication requests
- Authentication attempts followed by privilege escalation activities
SIEM Query:
source="windows" event_id=4662 (object_type="DS-Replication-Get-Changes" OR object_type="DS-Replication-Get-Changes-All") | stats count by user, src_ip