CVE-2021-42278 Microsoft Active Directory Domain Services Privilege Escalation Vulnerability
Microsoft Active Directory Domain Services contains an unspecified vulnerability that allows for privilege escalation.
From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.
Should You Worry?
- CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 11 Apr 2022.
- CISA lists it as known to be used in ransomware campaigns.
- Rated High severity (CVSS 7.5, scored by Vendor).
- It has been in the catalogue for 1,670 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
Active Directory Domain Services Elevation of Privilege Vulnerability
Affected Versions
| Product | Versions |
|---|---|
| Microsoft Windows Server 2008 R2 Service Pack 1 | 6.1.7601.0 to before 6.1.7601.25769 |
| Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation) | 6.1.7601.0 to before 6.1.7601.25769 |
| Microsoft Windows Server 2008 Service Pack 2 | 6.0.6003.0 to before 6.0.6003.21282 |
| Microsoft Windows Server 2008 Service Pack 2 (Server Core installation) | 6.0.6003.0 to before 6.0.6003.21282 |
| Microsoft Windows Server 2012 | 6.2.9200.0 to before 6.2.9200.23517 |
| Microsoft Windows Server 2012 (Server Core installation) | 6.2.9200.0 to before 6.2.9200.23517 |
From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.
What To Do Now
- 1
Find it
Search your asset inventory and external attack surface for Microsoft Active Directory. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management - 2
- 3
Hunt for compromise
If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.
Incident Response - 4
Prove it is fixed
Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.
Penetration Testing
Vendor Advisories
The Compliance Clock
General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.
Not Sure If You Are Exposed?
Our attack surface and vulnerability teams can check your internet-facing estate for CVE-2021-42278 and every other exploited flaw on the list.