---
id: "CVE-2026-123384"
page: "https://infrastack.ai/live/CVE-2026-123384"
kind: "vulnerability"
aliases: ["CVE-2026-123384"]
title: "Microsoft Outlook: heap overflow lets an unauthenticated attacker run code remotely"
severity: "high"
cvss: 8.8
epss: null
exploited: false
status: "open"
category: "vendor"
products: [{"name": "Microsoft Office LTSC 2021", "fixed": ["16.0.14334.21048"], "affected": ">= 16.0.1, < 16.0.14334.21048", "ecosystem": "vendor"}, {"name": "Microsoft Office LTSC 2024", "fixed": ["16.0.17932.21140"], "affected": ">= 16.0.0, < 16.0.17932.21140", "ecosystem": "vendor"}, {"name": "Microsoft 365 Apps for Enterprise", "fixed": [], "affected": "see https://aka.ms/OfficeSecurityReleases", "ecosystem": "vendor"}]
ecosystems: []
tags: ["microsoft-office", "outlook", "user-interaction", "vendor", "windows"]
not_affected_if: []
published_at: "2026-11-10T19:20:41+00:00"
first_seen_at: "2026-11-10T19:25:12+00:00"
updated_at: "2026-11-10T21:32:22+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123384", "first_seen_at": "2026-11-10T19:25:12+00:00"}, {"source": "analyst", "url": "https://app.opencve.io/cve/CVE-2026-123384", "first_seen_at": "2026-11-10T21:32:22+00:00", "cites": ["https://app.opencve.io/cve/CVE-2026-123384", "https://nvd.nist.gov/vuln/detail/CVE-2026-123384"]}]
exploit_sources: []
---

# Microsoft Outlook: heap overflow lets an unauthenticated attacker run code remotely

Link for people: https://infrastack.ai/live/CVE-2026-123384 (this .md is for agents)

A heap-based buffer overflow in Microsoft Office Outlook lets an unauthorized attacker execute code over a network. Sources report CVSS 8.8 (high) and no known exploitation in the wild.

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

## Affected

- vendor:Microsoft Office LTSC 2021 affected >= 16.0.1, < 16.0.14334.21048 fixed 16.0.14334.21048
- vendor:Microsoft Office LTSC 2024 affected >= 16.0.0, < 16.0.17932.21140 fixed 16.0.17932.21140
- vendor:Microsoft 365 Apps for Enterprise affected see https://aka.ms/OfficeSecurityReleases fixed no fixed version listed

## How to check

In Outlook: File > Office Account > About Outlook and read the build number. Compare it with the fixed builds: LTSC 2021 16.0.14334.21048, LTSC 2024 16.0.17932.21140, Microsoft 365 Apps per https://aka.ms/OfficeSecurityReleases. Whether the preview pane is an attack vector is unknown; the CVSS vector says user interaction is required.

## Fix

Update Office to a build at or above the fixed one: LTSC 2021 16.0.14334.21048, LTSC 2024 16.0.17932.21140. For Microsoft 365 Apps, the CVE record points to https://aka.ms/OfficeSecurityReleases for the fixed build. Source is a CVE record mirror, not Microsoft's own page.

## Timeline

- 2026-11-10T19:25:12+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123384
- 2026-11-10T21:32:22+00:00 analyst https://app.opencve.io/cve/CVE-2026-123384 — MSRC page and NVD returned no text to me, so nothing verified. Fixed builds come from the CVE record (CNA Microsoft) as mirrored by OpenCVE; the MSRC entry still needs reading for preview pane and M365 channel builds. This is not the exploited Outlook zero-day from Patch Tuesday, which is CVE-2026-124194 (spoofing).

## Documents

- [describes] OpenCVE: CVE-2026-123384 (CVE record mirror) https://app.opencve.io/cve/CVE-2026-123384
- [describes] NVD: CVE-2026-123384 https://nvd.nist.gov/vuln/detail/CVE-2026-123384

## From the sources

Heap-based buffer overflow in Microsoft Office Outlook 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_