Microsoft AD FS: Denial of service through unrestricted resource allocation
Summary
Active Directory Federation Services (AD FS) in several Windows 10 and Windows Server versions does not limit resource allocation. An unauthenticated attacker on the network can exhaust resources and cause a denial of service. If AD FS is reachable from the internet, for example through a Web Application Proxy, the attack can be launched from outside. Only availability is affected, but a failed AD FS breaks federated sign-ins.
Affected
- Windows 10 Version 1607 (builds before 10.0.14393.9612)
- Windows 10 Version 1809 (builds before 10.0.17763.9376)
- Windows Server 2012 and 2012 R2 (builds before 6.2.9200.26434 and 6.3.9600.23470)
- Windows Server 2016 (builds before 10.0.14393.9612)
- Windows Server 2019 (builds before 10.0.17763.9376)
- Windows Server 2022 (builds before 10.0.20348.5761)
- Windows Server 2025 (builds before 10.0.26100.33650)
- Server Core installations of the affected Windows Server versions
Fixed in
Fixed builds according to the official CVE record: 10.0.14393.9612 (Windows 10 1607, Server 2016), 10.0.17763.9376 (Windows 10 1809, Server 2019), 6.2.9200.26434 (Server 2012), 6.3.9600.23470 (Server 2012 R2), 10.0.20348.5761 (Server 2022), 10.0.26100.33650 (Server 2025). The mapping to specific KB numbers is not confirmed; install the newest update available.
Workaround
Unknown. No vendor or third-party mitigation was found in the sources. Apply the Microsoft update.
Exploitation
- CISA SSVC: exploitation none, automatable yes, technical impact partial.
- No public exploit found in the searches performed; this check is not exhaustive.
- Not listed in the CISA KEV catalog at the time of research.
Our recommendation
- Check whether AD FS runs on your systems and whether it is reachable from the internet, including via Web Application Proxy.
- Install the Microsoft update from the MSRC advisory on all affected AD FS servers and verify the build number.
- Plan a migration away from Windows 10 1607 (end of life) and Windows Server 2016 (support ends January 2027).
- Monitor AD FS availability and resource usage.
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-2026-85319 msrc.microsoft.com
- NVD record via Vulners vulners.com
- Microsoft advisory via Vulners vulners.com
- OpenCVE record CVE-2026-85319 app.opencve.io
- Strix CVE record CVE-2026-85319 www.strix.ai
- Windows 10 1607 security update KB5126868 support.microsoft.com
- Windows release health information learn.microsoft.com
- Windows 10 version history en.wikipedia.org
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, 18:37.
Original description (NVD)
Allocation of resources without limits or throttling 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.
Affected? We can help.
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