---
id: "CVE-2026-123383"
page: "https://infrastack.ai/live/CVE-2026-123383"
kind: "vulnerability"
aliases: ["CVE-2026-123383"]
title: "Microsoft Outlook: heap buffer overflow lets a remote attacker run code"
severity: "high"
cvss: 8.8
epss: null
exploited: false
status: "open"
category: "package"
products: [{"name": "Microsoft Office Outlook", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "Microsoft 365 Apps for Enterprise", "fixed": ["16.0.14334.21048", "16.0.17932.21140"], "affected": "unknown; builds before 16.0.14334.21048 / 16.0.17932.21140 per OffSeq (unconfirmed)", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["microsoft-office", "outlook", "package", "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: "2026-11-10T21:33:20+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123383", "first_seen_at": "2026-11-10T19:25:12+00:00"}, {"source": "analyst", "url": "https://radar.offseq.com/threat/cve-2026-123383-cwe-122-heap-based-buffer-overflow-in-microsoft-microsoft-365-apps-for-enterprise-b8f6bc38ad22d14e", "first_seen_at": "2026-11-10T21:33:20+00:00", "cites": ["https://radar.offseq.com/threat/cve-2026-123383-cwe-122-heap-based-buffer-overflow-in-microsoft-microsoft-365-apps-for-enterprise-b8f6bc38ad22d14e"]}]
exploit_sources: []
---

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

Link for people: https://infrastack.ai/live/CVE-2026-123383 (this .md is for agents)

A heap-based buffer overflow in Microsoft Office Outlook lets an unauthorized attacker reach code execution over a network. The NVD entry gives a CVSS score of 8.8 and does not describe the trigger in detail.

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

## Affected

- vendor:Microsoft Office Outlook affected range not listed fixed no fixed version listed
- vendor:Microsoft 365 Apps for Enterprise affected unknown; builds before 16.0.14334.21048 / 16.0.17932.21140 per OffSeq (unconfirmed) fixed 16.0.14334.21048, 16.0.17932.21140

## How to check

Check your Microsoft 365 Apps build (Outlook: File > Office Account > About Outlook). A secondary source (OffSeq, not Microsoft) lists fixed builds 16.0.14334.21048 and 16.0.17932.21140; confirm against the MSRC update guide entry for CVE-2026-123383 and the Office security release notes (learn.microsoft.com/officeupdates/microsoft365-apps-security-updates) before relying on them. Trigger needs user interaction per the CVSS vector (UI:R).

## Timeline

- 2026-11-10T19:25:12+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123383
- 2026-11-10T21:33:20+00:00 analyst https://radar.offseq.com/threat/cve-2026-123383-cwe-122-heap-based-buffer-overflow-in-microsoft-microsoft-365-apps-for-enterprise-b8f6bc38ad22d14e — MSRC and NVD pages returned nothing via web-cli; only secondary source found (OffSeq, linked as mentions). Nothing verified. Fix builds are from OffSeq only. Not known exploited per OffSeq.

## Documents

- [mentions] OffSeq: CVE-2026-123383 Microsoft 365 Apps heap-based buffer overflow https://radar.offseq.com/threat/cve-2026-123383-cwe-122-heap-based-buffer-overflow-in-microsoft-microsoft-365-apps-for-enterprise-b8f6bc38ad22d14e

## 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_