CVE-2026-56155 Microsoft Active Directory Federation Services Insufficient Granularity of Access Control Vulnerability
Microsoft Active Directory Federation Services contains an insufficient granularity of access control vulnerability that allows an authorized attacker to elevate privileges locally.
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 14 Jul 2026.
- Rated High severity (CVSS 7.8, scored by Vendor).
- It has been in the catalogue for 115 days. Systems still unpatched now have almost certainly been scanned for it.
What It Is
Insufficient granularity of access control in Active Directory Federation Services (AD FS) allows an authorized attacker to elevate privileges locally.
Affected Versions
| Product | Versions |
|---|---|
| Microsoft Windows 10 Version 1607 | 10.0.14393.0 to before 10.0.14393.9339 |
| Microsoft Windows 10 Version 1809 | 10.0.17763.0 to before 10.0.17763.9020 |
| Microsoft Windows Server 2012 | 6.2.9200.0 to before 6.2.9200.26226 |
| Microsoft Windows Server 2012 (Server Core installation) | 6.2.9200.0 to before 6.2.9200.26226 |
| Microsoft Windows Server 2012 R2 | 6.3.9600.0 to before 6.3.9600.23291 |
| Microsoft Windows Server 2012 R2 (Server Core installation) | 6.3.9600.0 to before 6.3.9600.23291 |
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 Federation Services. Include cloud images, appliances and anything a supplier runs for you.
Attack Surface Management - 2
Fix it
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Vulnerability Management - 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
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-2026-56155 and every other exploited flaw on the list.
Sources
- CISA Known Exploited Vulnerabilities catalogue
- NVD: CVE-2026-56155
- CVE record: CVE-2026-56155
- FIRST EPSS
- msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-56155
- learn.microsoft.com/en-us/windows-server/identity/ad-fs/decommission/adfs-decommission-guide
- msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56155