Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Network-reachable AD FS endpoint, unauthenticated and no user interaction (PR:N/UI:N), low complexity; impact limited to service crash so A:H with C:N/I:N.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
2DescriptionCVE.org
Stack-based buffer overflow in Active Directory Federation Services (AD FS) allows an unauthorized attacker to deny service over a network.
AnalysisAI
Denial of service in Microsoft Active Directory Federation Services (AD FS) allows a remote, unauthenticated attacker to crash the service by sending crafted network input that overflows a stack buffer (CWE-121). Because AD FS commonly fronts single sign-on for Microsoft 365, Azure AD, and federated web applications, an outage cascades into loss of authentication for every relying-party application. There is no public exploit identified at time of analysis and the flaw is not in CISA KEV; a Microsoft patch is available, and the CVSS 3.1 score is 7.5 (availability-only impact).
Technical ContextAI
AD FS is Microsoft's on-premises claims-based identity and federation server that issues security tokens (WS-Federation, WS-Trust, SAML, OAuth/OIDC) so users can single-sign-on to internal and cloud applications. The root cause is CWE-121, a stack-based buffer overflow: attacker-influenced data is copied into a fixed-size buffer on the call stack without adequate bounds checking, corrupting adjacent stack memory such as the return address or stack canary and terminating the process. The affected code ships as an OS role across a broad Windows range - per the supplied CPE and tag data this spans Windows Server 2012, 2012 R2, 2016, 2019, 2022 and 2025 (including Server Core installations), and the servicing tags also list Windows 10 (1607, 1809, 21H2, 22H2) and Windows 11 (24H2, 25H2, 26H1), reflecting Microsoft's shared servicing stack. Here the corruption is reported only to crash the service rather than to achieve control-flow hijack, so impact is confined to availability.
RemediationAI
Apply the Microsoft security update for CVE-2026-50411 to every affected Windows host running the AD FS role: Vendor-released patch available per Microsoft advisory (Patch available per vendor advisory) - obtain the exact KB/build for your OS version from https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-50411 and deploy via Windows Update, WSUS, or your patch-management pipeline, prioritizing internet-facing AD FS servers and Web Application Proxy (WAP) instances first. As interim compensating controls until patching completes, restrict network reachability to the AD FS/WAP endpoints - limit exposure of the federation service to only required relying-party networks and place the WAP behind rate-limiting/WAF filtering (trade-off: overly strict filtering can break legitimate federated logins, so test with real SSO flows), and ensure AD FS service auto-restart and monitoring are configured so a crash is recovered quickly (trade-off: restart masks but does not prevent repeated DoS). Do not rely on workarounds as a permanent fix; the patch is the authoritative remediation.
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Same weakness CWE-121 – Stack-based Buffer Overflow
View allSame technique Buffer Overflow
View allShare
External POC / Exploit Code
Leaving vuln.today
EUVD-2026-44073
GHSA-576r-hwq5-jr7g