---
id: "CVE-2026-123377"
page: "https://infrastack.ai/live/CVE-2026-123377"
kind: "vulnerability"
aliases: ["CVE-2026-123377"]
title: "Microsoft Outlook: heap buffer overflow lets a network attacker run code"
severity: "high"
cvss: 8.8
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["microsoft-office", "outlook", "package", "user-interaction", "windows"]
not_affected_if: []
published_at: "2026-11-10T19:20:40+00:00"
first_seen_at: "2026-11-10T19:25:12+00:00"
updated_at: "2026-11-10T21:34:30+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123377", "first_seen_at": "2026-11-10T19:25:12+00:00"}, {"source": "analyst", "url": "https://learn.microsoft.com/en-us/officeupdates/microsoft365-apps-security-updates", "first_seen_at": "2026-11-10T21:34:30+00:00", "cites": ["https://learn.microsoft.com/en-us/officeupdates/microsoft365-apps-security-updates"]}]
exploit_sources: []
---

# Microsoft Outlook: heap buffer overflow lets a network attacker run code

Link for people: https://infrastack.ai/live/CVE-2026-123377 (this .md is for agents)

A heap-based buffer overflow in Microsoft Office Outlook lets an unauthorized attacker run code over a network. Successful exploitation would give the attacker code execution on the affected machine.

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

## How to check

In Outlook: File > Office Account > About Outlook, and compare the version/build with the fixed builds in the Nov 10, 2026 Office security release notes for your channel. A lower build is exposed.

## Fix

Install the November 10, 2026 Microsoft 365 Apps / Office update: e.g. Current Channel 2610 build 20527.20196; Monthly Enterprise 2610 20527.20194, 2609 20430.20264, 2608 20326.20320; Office LTSC 2024 17932.21140; LTSC 2021 14334.21048; Office 2019 10417.20236. Microsoft's release notes list this CVE under Outlook for that release.

## Timeline

- 2026-11-10T19:25:12+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123377
- 2026-11-10T21:34:30+00:00 analyst https://learn.microsoft.com/en-us/officeupdates/microsoft365-apps-security-updates — Microsoft Office release notes (Nov 10, 2026) list this CVE under Outlook with fixed builds. MSRC page not retrievable, so affected ranges unknown; no exploitation or PoC found (the exploited Nov zero-day is a different Outlook spoofing CVE).

## Documents

- [fix] Microsoft Office security updates release notes (Nov 10, 2026) https://learn.microsoft.com/en-us/officeupdates/microsoft365-apps-security-updates

## From the sources

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

---

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