CVE-2026-50647: Active Directory Federation Server Denial of Service Vulnerability

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-14 · updated 2026-10-28
Weakness: CWE-835

Description

Loop with unreachable exit condition ('infinite loop') in Active Directory Federation Services (AD FS) allows an unauthorized attacker to deny service over a network.

Affected products

Microsoft .NET Framework: 4.8.1, 4.8, 4.6.2, 4.7, 4.7.1, 4.7.2 (+1)
Microsoft Windows 10 1607: before 10.0.14393.9339 — fixed in 10.0.14393.9339
Microsoft Windows 10: before 10.0.17763.9020 — fixed in 10.0.17763.9020
Microsoft Windows 10: before 10.0.19044.7548 — fixed in 10.0.19044.7548
Microsoft Windows 10: before 10.0.19045.7548 — fixed in 10.0.19045.7548
Microsoft Windows 11: before 10.0.26100.8875 — fixed in 10.0.26100.8875
Microsoft Windows 11 25H2: before 10.0.26200.8875 — fixed in 10.0.26200.8875
Microsoft Windows 11 version 26H1: before 10.0.28000.2525 — fixed in 10.0.28000.2525
Microsoft Windows Server 2012: r2
Microsoft Windows Server 2016: before 10.0.14393.9339 — fixed in 10.0.14393.9339
Microsoft Windows Server 2019: before 10.0.17763.9020 — fixed in 10.0.17763.9020
Microsoft Windows Server 2022: before 10.0.20348.5386 — fixed in 10.0.20348.5386
Microsoft Windows Server 2025: before 10.0.26100.33158 — fixed in 10.0.26100.33158
Microsoft .NET Framework 3.5 AND 4.7.2: from 4.7.0 before 2.0.50727.9069 & 3.0.30729.9067 & 4.7.4143.0 — fixed in 2.0.50727.9069 & 3.0.30729.9067 & 4.7.4143.0
Microsoft .NET Framework 3.5 AND 4.8: from 4.8.0 before 2.0.50727.9069 & 3.0.30729.9067 & 4.8.4803.0 — fixed in 2.0.50727.9069 & 3.0.30729.9067 & 4.8.4803.0
Microsoft .NET Framework 3.5 AND 4.8.1: from 4.8.1 before 2.0.50727.9182 & 3.0.30729.9168 & 4.8.9339.0 — fixed in 2.0.50727.9182 & 3.0.30729.9168 & 4.8.9339.0
Microsoft .NET Framework 4.6.2/4.7/4.7.1/4.7.2: from 4.7.0 before 4.7.4143.0 — fixed in 4.7.4143.0
Microsoft .NET Framework 4.8: from 4.8.0 before 4.8.4803.0 — fixed in 4.8.4803.0
Microsoft .NET Framework 4.8.1: from 4.8.0.0 before 4.8.9340.0 — fixed in 4.8.9340.0
Microsoft Windows 10 1607: from 10.0.14393.0 before 10.0.14393.9339 — fixed in 10.0.14393.9339
Microsoft Windows 10: from 10.0.17763.0 before 10.0.17763.9020 — fixed in 10.0.17763.9020
Microsoft Windows 10: from 10.0.19044.0 before 10.0.19044.7548 — fixed in 10.0.19044.7548
Microsoft Windows 10: from 10.0.19045.0 before 10.0.19045.7548 — fixed in 10.0.19045.7548
Microsoft Windows 11: from 10.0.26100.0 before 10.0.26100.8875 — fixed in 10.0.26100.8875
Microsoft Windows 11 25H2: from 10.0.26200.0 before 10.0.26200.8875 — fixed in 10.0.26200.8875
Microsoft Windows 11 version 26H1: from 10.0.28000.0 before 10.0.28000.2525 — fixed in 10.0.28000.2525
Microsoft Windows Server 2012: from 6.2.9200.0 before 6.2.9200.26226 — fixed in 6.2.9200.26226
Microsoft Windows Server 2012 R2: from 6.3.9600.0 before 6.3.9600.23291 — fixed in 6.3.9600.23291
Microsoft Windows Server 2016: from 10.0.14393.0 before 10.0.14393.9339 — fixed in 10.0.14393.9339
Microsoft Windows Server 2019: from 10.0.17763.0 before 10.0.17763.9020 — fixed in 10.0.17763.9020

How to fix

Upgrade to a fixed version: Microsoft Windows 10 1607 10.0.14393.9339; Microsoft Windows 10 10.0.17763.9020; Microsoft Windows 10 10.0.19044.7548; Microsoft Windows 10 10.0.19045.7548; Microsoft Windows 11 10.0.26100.8875; Microsoft Windows 11 25H2 10.0.26200.8875; Microsoft Windows 11 version 26H1 10.0.28000.2525; Microsoft Windows Server 2016 10.0.14393.9339; Microsoft Windows Server 2019 10.0.17763.9020; Microsoft Windows Server 2022 10.0.20348.5386; Microsoft Windows Server 2025 10.0.26100.33158; Microsoft .NET Framework 3.5 AND 4.7.2 2.0.50727.9069 & 3.0.30729.9067 & 4.7.4143.0. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-50647

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