EUVD-2026-43866
GHSA-39q5-6p3f-g6gf
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Unauthenticated network-reachable ADFS endpoint (AV:N/PR:N/UI:N) with a low-complexity request that crashes the service; pure DoS so C:N/I:N and A:H.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
2DescriptionCVE.org
Stack-based buffer overflow in Active Directory Federation Services allows an unauthorized attacker to deny service over a network.
AnalysisAI
Remote denial of service in Microsoft Active Directory Federation Services (ADFS) allows an unauthenticated network attacker to crash the service via a stack-based buffer overflow (CWE-121). The flaw affects the ADFS role across Windows Server 2012 through 2025 (and the underlying Windows 10 1607/1809 servicing components), carries a CVSS 7.5 availability-only score, and was reported by Microsoft with a patch available. There is no public exploit identified at time of analysis and it is not listed in CISA KEV.
Technical ContextAI
The vulnerability lies in Active Directory Federation Services, the Windows Server role that provides claims-based identity federation and single sign-on (SAML, WS-Federation, OAuth) to internal and external relying parties. Per the CPE data the affected code ships with Windows Server 2012, 2012 R2, 2016, and 2019 including Server Core installations, and per the tags Windows Server 2022 and 2025, plus the Windows 10 Version 1607 and 1809 servicing baselines. The root cause is CWE-121 (Stack-based Buffer Overflow): attacker-controlled input reaching an ADFS request parser is copied into a fixed-size stack buffer without adequate bounds checking, corrupting the stack and terminating the service process. Because ADFS federation endpoints are frequently published to the internet or a DMZ via Web Application Proxy to support external SSO, the network-reachable attack surface can be significant.
RemediationAI
Patch available per vendor advisory - apply the Microsoft security update for CVE-2026-50368 to all Windows Server systems running the ADFS role (2012, 2012 R2, 2016, 2019, 2022, and 2025, including Server Core installations) using the guidance at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-50368; the input does not include a specific KB or build number, so pull the exact patched build for each OS version from that advisory. As compensating controls until patching is complete, restrict network reachability of ADFS federation endpoints: place ADFS behind Web Application Proxy and limit external exposure of the /adfs/ endpoints, apply IP allow-listing or geo/rate-limiting at the perimeter or WAF to constrain who can reach the vulnerable parser, and enable ADFS service auto-recovery and monitoring so a crash is quickly restarted (trade-off: these controls shrink the attack surface but do not remove the flaw, and tightening endpoint access can break legitimate external federation partners). Migrating identity federation to Microsoft Entra ID where feasible removes the on-prem ADFS attack surface entirely but is a strategic change rather than an immediate fix.
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Same weakness CWE-121 – Stack-based Buffer Overflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
Leaving vuln.today