CVE-2026-85880

Windows Advanced Local Procedure Call (ALPC) Elevation of Privilege Vulnerability

CVE-2026-85880 is fixed in 20 products on 1 platform, first by KB5123099, released September 8, 2026. It is being exploited: CISA added it to the Known Exploited Vulnerabilities catalog on September 8, 2026. Patch Radar priority: Patch now.

Patch nowCISA KEV

CVSS

7.8

Important

Exploitation

Exploited

Reported by the vendor

CISA KEV

Sep 8, 2026

Federal due date Sep 22, 2026

EPSS

0.0039

33rd percentile

<p>Heap-based buffer overflow in Windows ALPC allows an authorized attacker to elevate privileges locally.</p>

Where it's fixed

Product	Fixed in	Fix	Released
Microsoft
Windows 10 Version 1607 for 32-bit Systems	14393.9512	KB5123099	Sep 8, 2026
Windows 10 Version 1607 for x64-based Systems	14393.9512	KB5123099	Sep 8, 2026
Windows 10 Version 1809 for 32-bit Systems	17763.9245	KB5122876	Sep 8, 2026
Windows 10 Version 1809 for x64-based Systems	17763.9245	KB5122876	Sep 8, 2026
Windows 10 Version 21H2 for 32-bit Systems		KB5122878	Sep 8, 2026
Windows 10 Version 21H2 for ARM64-based Systems		KB5122878	Sep 8, 2026
Windows 10 Version 21H2 for x64-based Systems		KB5122878	Sep 8, 2026
Windows 10 Version 22H2 for 32-bit Systems		KB5122878	Sep 8, 2026
Windows 10 Version 22H2 for ARM64-based Systems		KB5122878	Sep 8, 2026
Windows 10 Version 22H2 for x64-based Systems		KB5122878	Sep 8, 2026
Windows Server 2012		KB5123065	Sep 8, 2026
Windows Server 2012 (Server Core installation)		KB5123065	Sep 8, 2026
Windows Server 2012 R2		KB5123066	Sep 8, 2026
Windows Server 2012 R2 (Server Core installation)		KB5123066	Sep 8, 2026
Windows Server 2016	14393.9512	KB5123099	Sep 8, 2026
Windows Server 2016 (Server Core installation)	14393.9512	KB5123099	Sep 8, 2026
Windows Server 2019	17763.9245	KB5122876	Sep 8, 2026
Windows Server 2019 (Server Core installation)	17763.9245	KB5122876	Sep 8, 2026
Windows Server 2022	20348.5622	KB5122882	Sep 8, 2026
Windows Server 2022 (Server Core installation)	20348.5622	KB5122882	Sep 8, 2026

Details

Published
September 8, 2026
Weakness
Heap-based Buffer Overflow
CISA required action
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-85880

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