Microsoft Windows Heap-Based Buffer Overflow Vulnerability
TL;DR 📌
- Microsoft Windows Advanced Local Procedure Call contains a heap-based buffer overflow vulnerability that allows an attacker to elevate privileges locally.
- Highest CVSS: 7.8 (High).
- Listed in CISA KEV (2026-09-08) — this is being exploited in the wild.
- Fixed in
10.0.14393.9512,10.0.17763.9245,10.0.19044.7725,10.0.19045.7725— upgrade to this release or later. - CVEs: CVE-2026-85880.
What it is
CVE-2026-85880 is a heap-based buffer overflow in Windows Advanced Local Procedure Call (ALPC), the inter-process communication mechanism used by Windows components to pass requests between processes on the same machine.
The vector (AV:L/AC:L/PR:L/UI:N) shows this is a local, low-complexity attack requiring low-privilege access already on the box, with no user interaction needed. There’s no remote or network component here — an attacker needs to be running code locally, typically after gaining an initial foothold via some other means.
What they get is privilege escalation: successful exploitation grants high confidentiality, integrity, and availability impact (C:H/I:H/A:H), meaning full control gain rather than a partial or crash-only effect. This is a classic local-to-SYSTEM (or equivalent) escalation primitive, the kind of flaw used to turn a limited foothold into full administrative control.
This CVE is listed in CISA’s Known Exploited Vulnerabilities catalogue, added on 2026-09-08. It is known to be exploited.
What to do
- Patch to the fixed builds now: 10.0.14393.9512, 10.0.17763.9245, 10.0.19044.7725, 10.0.19045.7725, or 10.0.20348.5622, depending on your Windows version/branch.
- Treat this as a priority for any host where users or services run with standard (non-admin) privileges but could be chained with another foothold — ALPC-based privilege escalation is typically the second stage of an attack chain, not the entry point.
- Given the KEV listing, prioritise patching over other maintenance work on affected fleets; don’t wait for the next standard patch cycle.
- If patching is delayed on any endpoints, review local privilege boundaries and endpoint detection for unusual ALPC activity or unexpected privilege transitions, though no specific detection guidance is provided in the advisory.
- Confirm patch deployment against the exact build numbers above — general “latest cumulative update” language isn’t sufficient here given the specific fixed-version list Microsoft has published.
For leadership 🧭
Executive summary. This flaw turns any low-privilege foothold on a Windows machine into full administrative control, and it’s already on CISA’s exploited list. Patching should be treated as urgent across the fleet rather than folded into the next routine update cycle.
Why it matters:
- Windows ALPC is used constantly for inter-process communication, so the attack surface exists on essentially every Windows endpoint and server in the fleet.
- No user interaction and low complexity mean an attacker who has already landed a limited foothold can escalate to SYSTEM-equivalent control with minimal extra effort.
- It is listed in CISA’s Known Exploited Vulnerabilities catalogue, so this is not a theoretical risk sitting in a research paper.
- Full confidentiality, integrity and availability impact means successful exploitation gives an attacker complete control of the host, not just a crash or partial read.
Now / Next / Later:
- Now: Identify which Windows builds in your estate are below the fixed versions (10.0.14393.9512, 10.0.17763.9245, 10.0.19044.7725, 10.0.19045.7725, 10.0.20348.5622) and prioritise them for immediate patching.
- Next: Push the relevant cumulative updates to affected hosts in the next available change window, verifying against the exact build numbers rather than assuming ’latest update’ coverage.
- Later: Review privilege separation on endpoints where standard users run alongside services, and add detection for anomalous ALPC activity or unexpected privilege transitions to catch chained local-escalation attempts earlier.