CriticalCVE-2026-56155

    Active Directory Federation Services Elevation of Privilege Vulnerability (CVE-2026-56155)

    Published In CISA KEV since Sources: pwn.watch, Msrc Update Guide, CVE.org, BSI

    What is affected, what to do

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

    The vulnerability is being actively exploited; treat it as a priority. Update Microsoft Windows 10 Version 1607 to version 10.0.14393.9339, Microsoft Windows 10 Version 1809 to version 10.0.17763.9020, Microsoft Windows Server 2012 to version 6.2.9200.26226. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Microsoft Windows 10 Version 1607 lt 10.0.14393.0..10.0.14393.9339
    • Microsoft Windows 10 Version 1809 lt 10.0.17763.0..10.0.17763.9020
    • Microsoft Windows Server 2012 lt 6.2.9200.0..6.2.9200.26226
    • Microsoft Windows Server 2012 (Server Core installation) lt 6.2.9200.0..6.2.9200.26226
    • Microsoft Windows Server 2012 R2 lt 6.3.9600.0..6.3.9600.23291
    • Microsoft Windows Server 2012 R2 (Server Core installation) lt 6.3.9600.0..6.3.9600.23291
    • Microsoft Windows Server 2016 lt 10.0.14393.0..10.0.14393.9339
    • Microsoft Windows Server 2016 (Server Core installation) lt 10.0.14393.0..10.0.14393.9339
    • Microsoft Windows Server 2019 lt 10.0.17763.0..10.0.17763.9020
    • Microsoft Windows Server 2019 (Server Core installation) lt 10.0.17763.0..10.0.17763.9020
    • Microsoft Windows Server 2022 lt 10.0.20348.0..10.0.20348.5386
    • Microsoft Windows Server 2025 lt 10.0.26100.0..10.0.26100.33158
    • Microsoft Windows Server 2025 (Server Core installation) lt 10.0.26100.0..10.0.26100.33158
    Fixed in
    • Microsoft Windows 10 Version 1607 10.0.14393.9339
    • Microsoft Windows 10 Version 1809 10.0.17763.9020
    • Microsoft Windows Server 2012 6.2.9200.26226
    • Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.26226
    • Microsoft Windows Server 2012 R2 6.3.9600.23291
    • Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.23291
    • Microsoft Windows Server 2016 10.0.14393.9339
    • Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.9339
    • Microsoft Windows Server 2019 10.0.17763.9020
    • Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.9020
    • Microsoft Windows Server 2022 10.0.20348.5386
    • Microsoft Windows Server 2025 10.0.26100.33158
    • Microsoft Windows Server 2025 (Server Core installation) 10.0.26100.33158

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    Metrics

    7.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: pwn.watch, Msrc Update Guide, CVE.org, BSI

    0.4 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 28.0

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    166.14 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.4 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    28.0
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-1220

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw is only exploitable locally by an already authenticated user, but attackers use it as a second-stage step after initial access: SYSTEM on an AD FS server means theft of the token-signing key and the ability to mint SAML tokens for every federated application, Microsoft 365 included. Exploit code is functional and an official fix exists; the statistical exploitation model rates likelihood as fairly low, yet the KEV listing confirms targeted use, typically against organisations running hybrid identity. CISA reports no known ransomware use. If you run production AD FS, treat this as high-to-critical (Tier 0 crown jewel, patch within 72 h); hosts without the AD FS role can follow the regular patch cycle.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory every AD FS farm node and WAP server: run Get-WindowsFeature ADFS-Federation / Get-ADFSProperties, tag AD FS nodes as Tier 0, and compare the build (UBR in HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion) against the affected ranges.
      • Deploy the security update: target builds are Windows Server 2016 / Windows 10 1607: 10.0.14393.9339; Windows 10 1809: 10.0.17763.9020; Windows Server 2012 R2 (incl. Server Core): 6.3.9600.23291; Windows Server 2012 (incl. Server Core): 6.2.9200.26226. Look up the KB number in the Microsoft Security Update Guide entry for the CVE. Server 2012/2012 R2 require an active ESU subscription — without one, treat the host as unpatchable and schedule migration.
      • Restrict local logon rights on AD FS servers now: exploitation requires an authenticated local user. Audit local "Remote Desktop Users", "Administrators" and "Remote Management Users" and cut them down to named Tier 0 admins.
      • Hunt before you reboot: check each node for unknown local accounts, new services, scheduled tasks and group membership changes since the KEV listing; export event logs first.
      • If compromise is suspected: roll token-signing and token-decrypting certificates (Update-AdfsCertificate -CertificateType Token-Signing -Urgent), reset the AD FS service account/gMSA, and coordinate the certificate change with relying parties (including Entra ID/M365) — local privilege escalation on AD FS is a direct path to signing-key theft ("Golden SAML").

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: place AD FS in a dedicated Tier 0 segment; allow RDP 3389/tcp, WinRM 5985-5986/tcp and SMB 445/tcp only from PAWs or a hardened admin jump host. Expose only 443/tcp via Web Application Proxy.
      • IAM / least privilege: use GPO "Allow log on locally" / "Allow log on through Remote Desktop Services" scoped to a Tier 0 group, and explicitly deny Tier 1/2 accounts. Run the service as a gMSA with interactive logon denied.
      • Endpoint hardening: enforce WDAC/AppLocker on AD FS nodes (Microsoft-signed binaries plus approved admin tooling only). Enable LSA protection (RunAsPPL), Credential Guard and the ASR rule blocking credential theft from LSASS.
      • Protect key material: limit read access on the DKM container (CN=ADFS,CN=Microsoft,CN=Program Data,DC=…) to the AD FS service account and add a SACL for auditing; keep the token-signing key in an HSM where available.
      • Unpatchable hosts (2012/2012 R2 without ESU): prioritise migration to a supported OS; meanwhile no co-hosted roles and no non-admin local users.

    3. Runbook step 3

      Detection rules

      • Process ancestry (Sysmon EID 1 / Security 4688): cmd.exe, powershell.exe or rundll32.exe spawned by Microsoft.IdentityServer.ServiceHost.exe is high-fidelity. KQL: DeviceProcessEvents | where InitiatingProcessFileName =~ "Microsoft.IdentityServer.ServiceHost.exe" and FileName in~ ("cmd.exe","powershell.exe","rundll32.exe").
      • Host privilege escalation: Security 4672 for non-Tier-0 accounts, 4720/4732 (local account created / added to local admins), 7045 or 4697 (new service), 4698 (scheduled task) on AD FS nodes. Sigma shape: logsource: windows/security; selection: EventID: [4720,4732,4697,4698]; filter: Computer|contains: adfs.
      • Key-material access: Security 4662 on DCs for objects in the DKM container by any account other than the AD FS service account; Sysmon EID 10 targeting lsass.exe or the AD FS process from unsigned binaries; foreign processes connecting to the WID pipe \\.\pipe\microsoft##wid\tsql\query (Sysmon EID 17/18).
      • Token anomalies: enable AD FS auditing (Set-AdfsProperties -AuditLevel Verbose, auditpol /set /subcategory:"Application Generated" /success:enable /failure:enable) and baseline Security 1200/1202 by relying party and claims. In Entra ID, flag federated sign-ins with no matching AD FS 1200 event — a classic forged-token signal.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

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

    Source: pwn.watch, Microsoft Security Update Guide, CISA KEV Catalog, NVD (NIST), CVE.org (MITRE), cvelistv5, BSI WID Portal, BSI CSAF

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    MicrosoftWindows 10 Version 1607
    • 10.0.14393.0 – < 10.0.14393.9339
    • 10.0.14393.9339
    MicrosoftWindows 10 Version 1809
    • 10.0.17763.0 – < 10.0.17763.9020
    • 10.0.17763.9020
    MicrosoftWindows Server 2012
    • 6.2.9200.0 – < 6.2.9200.26226
    • 6.2.9200.26226
    MicrosoftWindows Server 2012 (Server Core installation)
    • 6.2.9200.0 – < 6.2.9200.26226
    • 6.2.9200.26226
    MicrosoftWindows Server 2012 R2
    • 6.3.9600.0 – < 6.3.9600.23291
    • 6.3.9600.23291
    MicrosoftWindows Server 2012 R2 (Server Core installation)
    • 6.3.9600.0 – < 6.3.9600.23291
    • 6.3.9600.23291
    MicrosoftWindows Server 2016
    • 10.0.14393.0 – < 10.0.14393.9339
    • 10.0.14393.9339
    MicrosoftWindows Server 2016 (Server Core installation)
    • 10.0.14393.0 – < 10.0.14393.9339
    • 10.0.14393.9339
    MicrosoftWindows Server 2019
    • 10.0.17763.0 – < 10.0.17763.9020
    • 10.0.17763.9020
    MicrosoftWindows Server 2019 (Server Core installation)
    • 10.0.17763.0 – < 10.0.17763.9020
    • 10.0.17763.9020
    MicrosoftWindows Server 2022
    • 10.0.20348.0 – < 10.0.20348.5386
    • 10.0.20348.5386
    MicrosoftWindows Server 2025
    • 10.0.26100.0 – < 10.0.26100.33158
    • 10.0.26100.33158
    MicrosoftWindows Server 2025 (Server Core installation)
    • 10.0.26100.0 – < 10.0.26100.33158
    • 10.0.26100.33158

    Vendors and products

    Affected operating systems

    Affected operating systems
    Windowsmicrosoftwindows_10_1607—
    Windowsmicrosoftwindows_10_1809—
    Windowsmicrosoftwindows_server_2012r2
    Windowsmicrosoftwindows_server_2012—
    Windowsmicrosoftwindows_server_2016—
    Windowsmicrosoftwindows_server_2019—
    Windowsmicrosoftwindows_server_2022—
    Windowsmicrosoftwindows_server_2025—

    Weakness classes (CWE)

    • CWE-1220Insufficient Granularity of Access Control

      Base

      The product implements access controls via a policy or other feature with the intention to disable or restrict accesses (reads and/or writes) to assets in a system from untrusted agents. However, implemented access controls lack required granularity, which renders the control policy too broad because it allows accesses from unauthorized agents to the security-sensitive assets.

      Entry at MITRE CWE-1220

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited

    References & sources

    • Microsoft Security Update GuideActive Directory Federation Services Elevation of Privilege VulnerabilityVendor advisory, Patch
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2026-56155government-resource
    • pwn.watchpwn.watch: Microsoft Active Directory Federation Services: Microsoft Active Directory Federation Services Insufficient Granularity of Access Control Vulnerability pwn-watch
    • Microsoft Security Update GuideMicrosoft Active Directory Federation Services — CVE-2026-56155pwn-watch
    • NVD (NIST)NVD: CVE-2026-56155pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
    • JPCERT/CCJPCERT/CC JPCERT-AT-2026-0020: Microsoft Releases July 2026 Security Updatesjpcert

    Linked advisories

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