---
id: "CVE-2026-120789"
page: "https://infrastack.ai/live/CVE-2026-120789"
kind: "vulnerability"
aliases: ["CVE-2026-120789"]
title: "Microsoft Excel: opening a crafted workbook can run attacker code (heap overflow)"
severity: "high"
cvss: 8.8
epss: null
exploited: false
status: "open"
category: "vendor"
products: []
ecosystems: []
tags: ["excel", "microsoft-office", "user-interaction", "vendor", "windows"]
not_affected_if: ["no-untrusted-spreadsheets"]
published_at: "2026-11-10T19:20:28+00:00"
first_seen_at: "2026-11-10T19:25:08+00:00"
updated_at: "2026-11-10T21:48:16+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-120789", "first_seen_at": "2026-11-10T19:25:08+00:00"}, {"source": "analyst", "url": "https://api.msrc.microsoft.com/sug/v2.0/en-US/vulnerability/CVE-2026-120789", "first_seen_at": "2026-11-10T21:48:16+00:00", "cites": ["https://api.msrc.microsoft.com/sug/v2.0/en-US/vulnerability/CVE-2026-120789"]}]
exploit_sources: []
---

# Microsoft Excel: opening a crafted workbook can run attacker code (heap overflow)

Link for people: https://infrastack.ai/live/CVE-2026-120789 (this .md is for agents)

Heap-based buffer overflow in Microsoft Office Excel (CWE-122). Microsoft rates it Critical RCE, CVSS 8.8. An attacker must convince a user to open a crafted workbook and interact with affected workbook features; code then runs as that user. Microsoft says not exploited, not publicly disclosed, 'Exploitation Less Likely'. Preview Pane is not an attack vector.

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

## How to check

In Excel: File > Account > About Excel, note the version/build and compare with the November 10, 2026 builds on Microsoft Learn 'Release notes for Microsoft Office security updates' (e.g. Current Channel 2610 build 20527.20196). Per-product affected/fixed builds are in the MSRC Security Update Guide for CVE-2026-120789 (JS-only page; not read in full).

## Fix

Install the November 2026 (2026-Nov, released 2026-11-10) Microsoft Office security update through Microsoft Update / Office updates. Microsoft marks customer action required. Exact fixed build per Office edition: see MSRC page for CVE-2026-120789; I did not confirm this CVE in the release-notes build list.

## Timeline

- 2026-11-10T19:25:08+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-120789
- 2026-11-10T21:48:16+00:00 analyst https://api.msrc.microsoft.com/sug/v2.0/en-US/vulnerability/CVE-2026-120789 — MSRC SUG API read: Nov 2026 Patch Tuesday, user opens crafted workbook, not exploited, Exploitation Less Likely. Affected builds/fixed builds not read, so fix and check not marked verified. Siblings CVE-2026-120785/6/8/90 look the same. No social search done (low volume).

## Documents

- [advisory] MSRC: Microsoft Office Excel Remote Code Execution Vulnerability CVE-2026-120789 https://api.msrc.microsoft.com/sug/v2.0/en-US/vulnerability/CVE-2026-120789

## From the sources

Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.

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_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_