Microsoft AD FS: Denial of service via excessive memory allocation
Summary
Active Directory Federation Services (AD FS), a Windows Server role for federated sign-in and single sign-on, contains a memory allocation with an excessive size value. An unauthorized attacker on the network can cause a denial of service, so AD FS sign-in becomes unavailable. No privileges or user interaction are required, and the impact is limited to availability. Exposure is highest for AD FS servers published to the internet.
Affected
- Windows Server 2012 and 2012 R2 (including Server Core): below 6.2.9200.26434 and below 6.3.9600.23470
- Windows 10 Version 1607 and Windows Server 2016 (including Server Core): below 10.0.14393.9612
- Windows 10 Version 1809 and Windows Server 2019 (including Server Core): below 10.0.17763.9376
- Windows Server 2022: below 10.0.20348.5761
- Windows Server 2025 (including Server Core): below 10.0.26100.33650
Fixed in
- Install the October 2026 security update for the affected Windows versions listed above.
- KB numbers per operating system: Unknown.
Workaround
- No vendor-specific workaround known.
- If AD FS is not required, disable or uninstall the AD FS role to remove the exposure.
Exploitation
- CISA SSVC: exploitation none, automatable yes, technical impact partial.
- Not listed in CISA KEV.
- VulDB reports no known exploit.
- No public proof of concept found in our searches; this does not prove that none exists.
Our recommendation
- Identify all AD FS servers and check whether they are reachable from the internet.
- Patch AD FS servers first, prioritising internet-facing systems, in the next maintenance window.
- Verify the patch level of the operating system on each AD FS server.
- Retire AD FS if it is no longer needed.
- Check the Windows 10 1607 support status with Microsoft before relying on it.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Denial of service – Active Directory Federation Services (AD FS)
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation unlikely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5126651, KB5126655, KB5126646, KB5126868, KB5126835, KB5126836
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-85324 msrc.microsoft.com
- OpenCVE: CVE-2026-85324 app.opencve.io
- Vulners NVD entry: CVE-2026-85324 vulners.com
- VulDB: CVE-2026-85324 vuldb.com
- Vulners MSCVE entry: MS:CVE-2026-85324 vulners.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 2 Nov 2026, 18:41.
Original description (NVD)
Memory allocation with excessive size value in Active Directory Federation Services (AD FS) allows an unauthorized attacker to deny service over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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