---
title: "CVE-2026-56155: Microsoft Active Directory Federation Services Insufficient Granularity of Access Control Vulnerability "
url: https://erroneo.us/security/cve/CVE-2026-56155/
description: "CVE-2026-56155 (Microsoft Active Directory Federation Services): Exploited in the wild (CISA KEV). Insufficient granularity of access control in Active…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-07-14
date_modified: 2026-10-21
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-56155"
kev: true
cvss: 7.8
epss: 0.00346
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-56155: Microsoft Active Directory Federation Services Insufficient Granularity of Access Control Vulnerability 

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Microsoft Active Directory Federation Services. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-07-14, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-07-28 ; treat that as the outer limit, not the target.
- EPSS 0.3% , percentile 27: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 27% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.
- Editorial verdict: Patch this week. AD FS CVE-2026-56155: Exploited EoP via Weak DKM Key ACLs — If you run AD FS, install the October 2026 or later Windows update on every farm server this week and confirm the DKM container ACL was fixed; unless you opted in, the July patch only flagged the weak permissions.

## What it is

Insufficient granularity of access control in Active Directory Federation Services (AD FS) allows an authorized attacker to elevate privileges locally.

## Affected products (CVE record)

- Microsoft Windows 10 Version 1607: 10.0.14393.0 < 10.0.14393.9339
- Microsoft Windows 10 Version 1809: 10.0.17763.0 < 10.0.17763.9020
- Microsoft Windows Server 2012: 6.2.9200.0 < 6.2.9200.26226
- Microsoft Windows Server 2012 (Server Core installation): 6.2.9200.0 < 6.2.9200.26226
- Microsoft Windows Server 2012 R2: 6.3.9600.0 < 6.3.9600.23291
- Microsoft Windows Server 2012 R2 (Server Core installation): 6.3.9600.0 < 6.3.9600.23291
- Microsoft Windows Server 2016: 10.0.14393.0 < 10.0.14393.9339
- Microsoft Windows Server 2016 (Server Core installation): 10.0.14393.0 < 10.0.14393.9339
- Microsoft Windows Server 2019: 10.0.17763.0 < 10.0.17763.9020
- Microsoft Windows Server 2019 (Server Core installation): 10.0.17763.0 < 10.0.17763.9020

## Severity

- microsoft CVSS 3.1: 7.8 `CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C`

## Exploitation

- CISA KEV: added 2026-07-14; federal due date 2026-07-28. Known ransomware use: Unknown.
- CISA required action: 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.
- CISA SSVC assessment: exploitation active , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.35% probability of exploitation activity in the next 30 days; percentile 27.

## Sources

- [Active Directory Federation Services Elevation of Privilege Vulnerability](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56155)
- [Listed in CISA KEV notes (msrc.microsoft.com)](https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-56155)
- [Listed in CISA KEV notes (learn.microsoft.com)](https://learn.microsoft.com/en-us/windows-server/identity/ad-fs/decommission/adfs-decommission-guide)
- [CVE.org record CVE-2026-56155](https://www.cve.org/CVERecord?id=CVE-2026-56155)
- [NVD entry CVE-2026-56155](https://nvd.nist.gov/vuln/detail/CVE-2026-56155)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-56155)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk)

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Source page: https://erroneo.us/security/cve/CVE-2026-56155/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt