Affects Microsoft Active Directory Federation Services (widely deployed enterprise auth/SSO); auth bypass and network spoofing can expose federated access across organizations.
CVE-2026-83674
AD FS authentication bypass enabling network spoofing and impersonation
Is CVE-2026-83674 being exploited?
Not confirmed. CVE-2026-83674 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.64% probability of exploitation in the next 30 days.
How severe is CVE-2026-83674?
CVE-2026-83674 is rated High with a CVSS score of 8.1. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-83674?
Yes. A fix has been recorded for CVE-2026-83674. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-83674 affect?
CVE-2026-83674 affects Microsoft Active Directory Federation Services (AD FS), Windows Server (AD FS role). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-83674?
Apply Microsoft AD FS security update immediately; restrict AD FS network exposure.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Authentication bypass via AD FS network spoofing, allowing attackers to impersonate users/services and access federated resources and SSO-protected apps.
Immediate action required
- affected>= 10.0.14393.0 and < 10.0.14393.9612
- affected>= 10.0.17763.0 and < 10.0.17763.9376
- affected>= 10.0.14393.0 and < 10.0.14393.9612
- affected>= 10.0.14393.0 and < 10.0.14393.9612
- affected>= 10.0.17763.0 and < 10.0.17763.9376
- affected>= 10.0.17763.0 and < 10.0.17763.9376
- affected>= 10.0.20348.0 and < 10.0.20348.5761
- affected>= 10.0.26100.0 and < 10.0.26100.33650
- affected>= 10.0.26100.0 and < 10.0.26100.33650
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.