PatchTheCVECVE-2026-56155: Microsoft Active Directory Federation Services Insufficient Granularity of Access Control Vulnerability
64
Patch now
HIGH 7.8EXPLOITEDWATCHLISTUPGRADEUPGRADEMITIGATE
CVE-2026-56155 is a high-severity flaw (CVSS 7.8) affecting windows 10 1607, windows 10 1809, windows server 2012, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
Insufficient granularity of access control in Active Directory Federation Services (AD FS) allows an authorized attacker to elevate privileges locally.
Why this priority
- High severity
- Exploited in the wild (CISA KEV)
- On your watchlist
A fixed release or distro patch exists.
Risk facts
| CVSS score | 7.8 (High) |
| Attack vector | Local |
| Attack complexity | Low |
| Privileges needed | Low |
| User interaction | None |
| EPSS exploit chance | 0.3% (top 72%) |
| CISA exploited list | Yes, fix due 2026-07-28 |
| Weakness | CWE-1220 |
| Published | 2026-07-14 |
| Last modified | 2026-07-15 |
Publisher (CNA): Microsoft Corporation · Vendor: microsoft
Last updated 2026-07-15 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
- Exploited Added to the CISA Known Exploited Vulnerabilities list
- Published CVE record published
- Updated Record last modified
- Deadline CISA due date for US federal agencies to patch
microsoft windows 10 1607 UPGRADE
Affected: < 10.0.14393.9339
Fixed in: 10.0.14393.9339
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
microsoft windows 10 1809 UPGRADE
Affected: < 10.0.17763.9020
Fixed in: 10.0.17763.9020
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
microsoft windows server 2012 MITIGATE
Affected: all versions · r2
Fixed in: no fixed release known
Safe to downgrade to: a release before r2
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
microsoft windows server 2016 UPGRADE
Affected: < 10.0.14393.9339
Fixed in: 10.0.14393.9339
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
microsoft windows server 2019 UPGRADE
Affected: < 10.0.17763.9020
Fixed in: 10.0.17763.9020
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
microsoft windows server 2022 UPGRADE
Affected: < 10.0.20348.5386
Fixed in: 10.0.20348.5386
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
Exact fixes by distribution
A distro patch exists: prefer upgrading over downgrading.
Fedora 46 · gcl · FIXED · 2.7.1-12.fc46 · FEDORA-2026-ff383a759b · source
sudo dnf upgrade --advisory=FEDORA-2026-ff383a759b
Fedora ELN · mozjs140 · FIXED · 140.13.0-5.eln159 · FEDORA-2026-f7ed0026e0 · source
sudo dnf upgrade --advisory=FEDORA-2026-f7ed0026e0
Windows 10 Version 1809 for 32-bit Systems · KB5099538 · FIXED · 10.0.17763.9020 · KB5099538 · source
Install KB5099538 via Windows Update, then verify:
Get-HotFix -Id KB5099538
Windows 10 Version 1809 for x64-based Systems · KB5099538 · FIXED · 10.0.17763.9020 · KB5099538 · source
Install KB5099538 via Windows Update, then verify:
Get-HotFix -Id KB5099538
Install KB5099538 via Windows Update, then verify:
Get-HotFix -Id KB5099538
Windows Server 2019 (Server Core installation) · KB5099538 · FIXED · 10.0.17763.9020 · KB5099538 · source
Install KB5099538 via Windows Update, then verify:
Get-HotFix -Id KB5099538
Install KB5099540 via Windows Update, then verify:
Get-HotFix -Id KB5099540
Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-56155?
windows 10 1607: upgrade to 10.0.14393.9339; windows 10 1809: upgrade to 10.0.17763.9020; windows server 2012: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2026-56155 being exploited?
Yes. CVE-2026-56155 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.
What does CVE-2026-56155 affect?
CVE-2026-56155 affects windows 10 1607, windows 10 1809, windows server 2012. Severity is high (CVSS 7.8). Insufficient granularity of access control in Active Directory Federation Services (AD FS) allows an authorized attacker to elevate privileges locally.
How urgent is CVE-2026-56155?
Priority 64/100. High severity; Exploited in the wild (CISA KEV); On your watchlist
Software pages
Windows vulnerabilities · Windows Server vulnerabilities · Active Directory vulnerabilities
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