fixnx
criticalCISA KEVCVE-2026-56155

CVE-2026-56155 in Active Directory Federation Services

Microsoft Active Directory Federation Services contains an insufficient granularity of access control vulnerability that allows an authorized attacker to elevate privileges locally.

ProductActive Directory Federation Services
CVSS7.8
EPSSNot scored yet
UpdatedJuly 15, 2026

Quick answer

Microsoft Active Directory Federation Services should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.

Who is affected

Affected versions

  • AD FS on Windows Server 2012 ESU, 2012 R2 ESU, 2016, 2019, 2022, version 23H2, and 2025 before the July 14, 2026 security update

Fixed versions

  • July 14, 2026 Windows security update or later
  • DKM ACL remediation per Microsoft KB5121391 when Event ID 1132 is logged

How to fix it

CVE-2026-56155 affects Active Directory Federation Services. In simple terms, a user may get access or settings they should not have. Fix it by updating to July 14, 2026 Windows security update or later; DKM ACL remediation per Microsoft KB5121391 when Event ID 1132 is logged. If this system is online or used by admins, treat the fix as urgent.

  1. Find every place where Active Directory Federation Services is installed or used.
  2. Check if the version matches: AD FS on Windows Server 2012 ESU, 2012 R2 ESU, 2016, 2019, 2022, version 23H2, and 2025 before the July 14, 2026 security update.
  3. Update or apply the vendor fix: July 14, 2026 Windows security update or later; DKM ACL remediation per Microsoft KB5121391 when Event ID 1132 is logged.
  4. If you cannot update today, allow only trusted users and trusted networks.
  5. Turn off the affected feature or plugin if the vendor says that is safe to do.
  6. Check logs for crashes, strange requests, new admin actions, or unexpected access.
  7. Change secrets or passwords if you think data or admin access may have been exposed.

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Verify the fix

  • Confirm the installed version or mitigation matches: July 14, 2026 Windows security update or later; DKM ACL remediation per Microsoft KB5121391 when Event ID 1132 is logged.
  • Confirm the affected feature is no longer exposed to untrusted users.
  • Run the affected workflow again and make sure it still works.
  • Review logs again after the fix for repeated suspicious activity.
  • Run a new Fixnx scan if this software is part of a public website.
  • Save the advisory link and proof of the fix in your change record.

Related categories

WindowsMicrosoftAuthorization BypassPrivilege Escalation

Trusted references

Source advisoryNVD, CISA KEVSource advisoryNVD, CISA KEVSource advisoryNVD, CISA KEVCISA KEV entryNVD, CISA KEV

FAQ

What is affected by CVE-2026-56155?

Microsoft Active Directory Federation Services versions listed as affected should be reviewed: AD FS on Windows Server 2012 ESU, 2012 R2 ESU, 2016, 2019, 2022, version 23H2, and 2025 before the July 14, 2026 security update.

What should I fix first?

Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.

How do I confirm the fix worked?

Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.

How are Fixnx security risk categories chosen?

Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.