CVE-2026-83646: Active Directory Federation Services (AD FS) Spoofing Vulnerability

Overview

Severity

Medium (CVSS 4.8)

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N/E:U/RL:O/RC:C

Category

Spoofing

Exploit Status

Not Exploited

Exploitation Likelihood

Unlikely

Patch Tuesday

2026-Oct

Released

2026-10-13

Description

Url redirection to untrusted site ('open redirect') in Active Directory Federation Services (AD FS) allows an authorized attacker to perform spoofing over a network.

Affected Products (12)

Windows

• Windows 10 Version 1809 for 32-bit Systems
• Windows 10 Version 1809 for x64-based Systems
• Windows Server 2019
• Windows Server 2019 (Server Core installation)
• Windows Server 2022
• Windows Server 2022 (Server Core installation)
• Windows Server 2025 (Server Core installation)
• Windows Server 2025
• Windows 10 Version 1607 for 32-bit Systems
• Windows 10 Version 1607 for x64-based Systems
• Windows Server 2016
• Windows Server 2016 (Server Core installation)

Security Updates (4)

• 5126651
• 5126655
• 5126646
• 5126868

Revision History

• 2026-10-13: Information published.