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CVE-2026-56155

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Microsoft Active Directory Federation Services. For every flaw being used in attacks, see Exploited flaws; for Microsoft’s, see Microsoft flaws being used in attacks.

CVE-2026-56155 is a security flaw in Microsoft Active Directory Federation Services, the system companies use to manage staff accounts and computers. Someone who already has a foothold can use Microsoft Active Directory Federation Services to take full control of the machine. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 14 Jul 2026.[1]

Microsoft Active Directory Federation Services is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 10.0.14393.9339, 10.0.17763.9020, 6.2.9200.26226 and 6.3.9600.23291.

Description

CISA calls it an insufficient granularity of access control in Microsoft Active Directory Federation Services. In its words: “Microsoft Active Directory Federation Services contains an insufficient granularity of access control vulnerability that allows an authorized attacker to elevate privileges locally.”[1]

The underlying weakness is CWE-1220, in MITRE’s list of common software weaknesses.[2]

It scores 7.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by the organisation that published the CVE using CVSS 3.1.[2]

Affected versions

NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]

ProductFixed in
Windows 10 Version 160710.0.14393.9339
Windows 10 Version 180910.0.17763.9020
Windows Server 20126.2.9200.26226
Windows Server 2012 (Server Core installation)6.2.9200.26226
Windows Server 2012 R26.3.9600.23291
Windows Server 2012 R2 (Server Core installation)6.3.9600.23291
Windows Server 201610.0.14393.9339
Windows Server 2016 (Server Core installation)10.0.14393.9339

Most families won’t have Microsoft Active Directory Federation Services; it’s for whoever looks after IT at work.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 14 Jul 2026, within a day of it being made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 28 Jul 2026 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at under 1%. That’s in the top 72% of the flaws it scores.[4]

CISA assesses it as not automatable: each attack takes some work.

CISA doesn’t say who was attacked, or how.

Fix

Microsoft has published a fix or advice.[3] CISA’s 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).”[1]

  1. Check whether you use it.Microsoft Active Directory Federation Services is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
  2. Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 10.0.14393.9339, 10.0.17763.9020, 6.2.9200.26226 and 6.3.9600.23291), or not in use. CISA gave US government agencies until 28 Jul 2026 to fix it.
  3. If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.

You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 7.8.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at under 1%.[4]

See also

Other Microsoft flaws

  • CVE-2026-96951, Microsoft Windows: command injection ·
  • CVE-2026-65660, Microsoft SharePoint: code injection ·
  • CVE-2026-85880, Microsoft Windows: heap-based buffer overflow ·
  • CVE-2026-81963, Microsoft Windows: link following ·
  • CVE-2019-1068, Microsoft SQL Server: remote code execution ·

Similar flaws

  • CVE-2025-31201, Apple devices: arbitrary read and write ·

Added the same day

  • CVE-2026-56164, Microsoft SharePoint Server: missing authentication for critical function ·
  • CVE-2026-15410, SonicWall SMA1000 Appliances: code injection ·
  • CVE-2026-15409, SonicWall SMA1000 Appliances: server-side request forgery ·

Every Microsoft flaw on CISA’s list · Everything added in July 2026

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Microsoft Active Directory Federation Services Insufficient Granularity of Access Control Vulnerability”. Known Exploited Vulnerabilities Catalog, added 14 Jul 2026.
  2. ^ National Institute of Standards and Technology. “CVE-2026-56155 Detail”. National Vulnerability Database, published 14 Jul 2026.
  3. ^ Microsoft. Advisories and fixes: msrc.microsoft.com, learn.microsoft.com, msrc.microsoft.com.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.003, percentile 28.2, 31 Oct 2026.
  5. CVE Program. “CVE-2026-56155”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.