---
id: "CVE-2026-85880"
kind: "vulnerability"
aliases: ["CVE-2026-85880"]
title: "Heap-based buffer overflow in Windows ALPC allows an authorized attacker to elevate privileges locally"
severity: "high"
cvss: 7.8
epss: null
exploited: true
status: "resolved"
category: "vendor"
products: [{"name": "Microsoft Windows", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "Windows 10 22H2/21H2", "fixed": ["10.0.19045.7725"], "affected": ">= 10.0.19044.0, < 10.0.19045.7725", "ecosystem": "vendor"}, {"name": "Windows 10 1607 / Windows Server 2016", "fixed": ["10.0.14393.9512"], "affected": ">= 10.0.14393.0, < 10.0.14393.9512", "ecosystem": "vendor"}, {"name": "Windows 10 1809 / Windows Server 2019", "fixed": ["10.0.17763.9245"], "affected": ">= 10.0.17763.0, < 10.0.17763.9245", "ecosystem": "vendor"}, {"name": "Windows Server 2012 R2", "fixed": ["6.3.9600.23398"], "affected": "< 6.3.9600.23398", "ecosystem": "vendor"}, {"name": "Windows Server 2012", "fixed": ["6.2.9200.26349"], "affected": "< 6.2.9200.26349", "ecosystem": "vendor"}, {"name": "microsoft windows 10 1607", "fixed": ["10.0.14393.9512"], "affected": "< 10.0.14393.9512", "ecosystem": "vendor"}, {"name": "microsoft windows 10 1809", "fixed": ["10.0.17763.9245"], "affected": "< 10.0.17763.9245", "ecosystem": "vendor"}, {"name": "microsoft windows 10 21h2", "fixed": ["10.0.19044.7725"], "affected": "< 10.0.19044.7725", "ecosystem": "vendor"}, {"name": "microsoft windows 10 22h2", "fixed": ["10.0.19045.7725"], "affected": "< 10.0.19045.7725", "ecosystem": "vendor"}, {"name": "microsoft windows server 2012", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "microsoft windows server 2012", "fixed": [], "affected": "= r2", "ecosystem": "vendor"}, {"name": "microsoft windows server 2016", "fixed": ["10.0.14393.9512"], "affected": "< 10.0.14393.9512", "ecosystem": "vendor"}, {"name": "microsoft windows server 2019", "fixed": ["10.0.17763.9245"], "affected": "< 10.0.17763.9245", "ecosystem": "vendor"}, {"name": "microsoft windows server 2022", "fixed": ["10.0.20348.5622"], "affected": "< 10.0.20348.5622", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "local", "microsoft-windows", "privilege-escalation", "sandbox-escape", "self-hosted", "vendor", "windows"]
not_affected_if: ["non-windows-systems", "patched-sep-2026"]
published_at: "2026-09-08T00:00:00+00:00"
first_seen_at: "2026-10-23T19:11:51+00:00"
updated_at: "2026-10-23T23:44:52+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-85880", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-10-23T21:39:11+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-85880", "first_seen_at": "2026-10-23T23:44:52+00:00"}]
---

# Heap-based buffer overflow in Windows ALPC allows an authorized attacker to elevate privileges locally

Heap-based buffer overflow in Windows ALPC. Code running in a low-privilege AppContainer can escape the sandbox and gain SYSTEM locally, with no user interaction. Microsoft reports exploitation detected; it is not publicly disclosed. Fixed in the Sep 8 2026 updates. CVSS 7.8.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Microsoft Windows affected ? fixed ?
- vendor:Windows 10 22H2/21H2 affected >= 10.0.19044.0, < 10.0.19045.7725 fixed 10.0.19045.7725
- vendor:Windows 10 1607 / Windows Server 2016 affected >= 10.0.14393.0, < 10.0.14393.9512 fixed 10.0.14393.9512
- vendor:Windows 10 1809 / Windows Server 2019 affected >= 10.0.17763.0, < 10.0.17763.9245 fixed 10.0.17763.9245
- vendor:Windows Server 2012 R2 affected < 6.3.9600.23398 fixed 6.3.9600.23398
- vendor:Windows Server 2012 affected < 6.2.9200.26349 fixed 6.2.9200.26349
- vendor:microsoft windows 10 1607 affected < 10.0.14393.9512 fixed 10.0.14393.9512
- vendor:microsoft windows 10 1809 affected < 10.0.17763.9245 fixed 10.0.17763.9245
- vendor:microsoft windows 10 21h2 affected < 10.0.19044.7725 fixed 10.0.19044.7725
- vendor:microsoft windows 10 22h2 affected < 10.0.19045.7725 fixed 10.0.19045.7725
- vendor:microsoft windows server 2012 affected ? fixed ?
- vendor:microsoft windows server 2012 affected = r2 fixed ?
- vendor:microsoft windows server 2016 affected < 10.0.14393.9512 fixed 10.0.14393.9512
- vendor:microsoft windows server 2019 affected < 10.0.17763.9245 fixed 10.0.17763.9245
- vendor:microsoft windows server 2022 affected < 10.0.20348.5622 fixed 10.0.20348.5622

## How to check

Run winver, or in PowerShell: [System.Environment]::OSVersion.Version. Compare the full build number with the fixed build, e.g. Win10 22H2 10.0.19045.7725, Server 2016/Win10 1607 10.0.14393.9512, Server 2012 R2 6.3.9600.23398, Server 2012 6.2.9200.26349. Or check that the Sep 2026 cumulative update is installed: Get-HotFix -Id KB5122878 (Win10 21H2/22H2), KB5122876 (1809), KB5123099 (2016/1607), KB5123066 (2012 R2), KB5123065 (2012), KB5122882 (Server 2022).

## Fix

Install the Sep 8 2026 Windows cumulative or monthly rollup update. KBs: KB5122878 (Win10 21H2/22H2), KB5122876 (Win10 1809 and Server 2019), KB5123099 (Server 2016 and Win10 1607), KB5123066 (Server 2012 R2), KB5123065 (Server 2012), KB5122882 (Server 2022). No workaround was found. CISA required action: apply the update under BOD 26-04 and the forensics triage requirements.

## Timeline

- 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-85880
- 2026-10-23T21:39:11+00:00 analyst — MSRC advisory (Sep 8 2026) read: ALPC heap overflow, AppContainer escape to SYSTEM, exploitation detected, not publicly disclosed. Builds from CVE record; KBs from Rapid7 (secondary). Win11 and 2019 fixed builds not read. No PoC link found; social search not done.
- 2026-10-23T23:44:52+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-85880

## Documents

- [advisory] MSRC: Windows ALPC Elevation of Privilege (CVE-2026-85880) https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-85880
- [describes] CVE record CVE-2026-85880 (affected builds) https://www.cve.org/CVERecord?id=CVE-2026-85880
- [fix] Rapid7 DB: CVE-2026-85880 (KB list) https://www.rapid7.com/db/vulnerabilities/cve-2026-85880/

## From the sources

Microsoft Windows Advanced Local Procedure Call contains a heap-based buffer overflow vulnerability that allows an attacker to elevate privileges locally.

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_